Member of ASTA, American Society of Travel Agents. Spain's travel rules have now returned to normal, as before the pandemic. Please check the travel requirements for your final destination. We have one API that does it all. Make travel easier for your clients by providing quick and convenient access to the travel documents they need. Please be aware that you need to meet these requirements to be able to travel: Please check the latest US entry requirements before you travel. Airport Airport (Within same country but different regions with no domestic info) Centers for Disease Control and Prevention, International Air Transport Association (IATA), Proof of citizenship, such as a government-issued photo ID and birth certificate with raised seal or a valid. Provide your customers with crucial entry information to mitigate trip disruptions and improve customer satisfaction. Quantity Limit 3 per customer. Example: A PCR_Test needs to be done 72 hours before departure. For more information on their restrictions and e-visa solutions, visit their website here. 2023 American Express. Even though a trip might be valid syntax, it might not provide the desired output. Likewise, if you were vaccinated in California, you can use the state's My Vaccination Record to show proof of vaccination. Text describing the vaccination rate has also been corrected to reflect that rates are for the full population. You can fast-track through the airport with VeriFLY priority lanes (available at selected airports). No, you must make two requests. Access your favorite topics in a personalized feed while you're on the go. Enable more online check-in opportunities for customers requiring eVisas and ensure there are no surprises during gate checks. For countries where eVisas arent yet available, our goal is to make the process of buying a paper visa as simple and hassle-free as possible. These restrictions can range from quarantining, to COVID-19 testing, to face mask mandates. Experience Platinum Princess By continuing to browse this site you agree to our use of. However, restrictions are constantly changing, which can put soon-to-be travelers in a difficult planning position leading up to their dream post-covid vacation. Should you choose to purchase a COVID-19 test from these suppliers, their terms and conditions will apply. We had probably every visa experience in the book, explains Tremaine in an interview with TravelPulse Canada last week. Check the expiration date on your passport carefully before traveling to Europe - especially children's passports, which are valid five years, not 10 years like those issued to U.S. citizens aged 16 and older. Sherpa Original Deluxe Travel Pet Carrier (Choose Size & Color) $33.99 - $49.99. Be prepared to show the following: These days, plans can change quickly from borders closing to your personal comfort level and COVID-19 status. Our extensive database includes passport and visa requirements, border procedures, health declarations, passenger locator forms, quarantine measures, transit restrictions and vaccination requirements, all in one dashboard. Need a visa to travel? Quick facts. You can find more information with an example for the testWindow here. Airlines update information on a regular basis. Some destinations allow restriction-free entry for vaccinated travelers, and some destinations may only exempt you from testing and/or quarantine. The company was growing, and had clients that included Iceland Air, Condor, Thomas Cook, G Adventures, kiwi.com and a variety of OTAs. It's easy to keep all your COVID-related documents in one place. Sherpa Travel Restrictions: Find latest travel and health restrictions for your trip Sherpa Travel Restrictions Find latest travel and health restrictions for your trip Tuesday, January 4, 2022 Visit Sherpa Travel Restrictions Recent startups Daft Art Outreach Grader Tales Factory Infinity Bot List Free UI Resources Ask Steve starter.place Country -> Country (same country) Please log in to Manage My Booking from 48 hours before departure and upload all travel documents required for your journey. Provided data in this page is compiled by Sherpa, and does not guarantee passenger's entry or exit. By clicking Sign up, you agree to receive marketing emails from Insider According to the International Air Transport Association (IATA), the risk of COVID-19 transmission in an airplane cabin environment even on long international flights is relatively low for several reasons, including the use of on-board HEPA filters, refreshed cabin air 20-30 times per hour, and the position of passengers. Hotel & Resort, Copyright 2023 Northstar Travel Media, LLC. eVisa & Travel Requirements Trip Element Quick Start, Content Security Policy for Safari Browser, Tutorial: Retrieving the Requirements for a Trip, Tutorial: Display the Groupings Recursively, Use Case: Get all VISA Requirements for All Countries, Use Case: Get VISA Requirements for a specific Country Example 1, Use Case: Get VISA Requirements for a specific Country Example 2, eVisa API - Application Widget Integration. Sherpa provides information in the body of the response, but there is no way to personalize the information based on traveller vaccine types. You remain subject to British Airways Terms and Conditions of Carriagewhich are applicable to your booking, including in relation to denied boarding for failure to meet country entry requirements. We are often the very first source to highlight changes in policies because we look at so much information. Build your brand as a trusted source. A place with a quarantine rule rated as far less accessible than one that could be entered with just a negative Covid-19 test. sherpa uses cookies to enhance your browsing experience. Half Day. You May Also Like Click here to learn more. Requirements may include temperature checks, proof of negative COVID-19 tests or completion of forms. These restrictions can range from quarantining, to COVID-19 testing, to face mask mandates. Confirm any destination-specific COVID-19 restrictions. Prices start at these amounts and are correct at time of publication. This attribute lists out when the test is to be done, the medical requirement type and how long. You can also contact your hotel directly to see how they are focusing on guest safety, which may include increased disinfection and cleaning, plexiglass barriers at check-in, contactless payment and more. If you booked through American Express Travel and have additional Coronavirus questions, feel free to visit us online or call the number on the back of your Card. Describing a Trip A Trip can be described using one or multiple Segment. Rather than focus solely on visa requirements, Sherpa morphed to also become an aggregate of COVID travel information. For example, many hotel properties continue to update their COVID-19 health and safety information, as well as other travel guidelines. Embed personalized data on your website, destination pages, mobile app, loyalty platform and manage booking platform or link to our co-branded WebAppand keep customers in the booking flow. Now more than ever, you may be ready to escape from it all with a great vacation. Transform an entry requirement into an ancillary revenue stream and enable your customers to move freely. The Visa requirements section can be found as part of the /V2/trips response or as a stand-alone request for entry requirements under the /v2/procedures resource endpoint. Sherpa aggregates millions of data points from thousands of sources including official Government websites and trusted 3rd party sources every day. If you're unable to travel? If youre in the business of tourism and travel, then this is for you. Travel rules remain the same within the same region. 1 in 2 international travellers will need an eVisa by 2023. get you started. Over 1.6 million people have used Expedia's tool since its pilot phase began in November 2020. Please review. Get a personalized demo Need a visa to travel? Condition New. COVID-19 Testing Requirements What type of COVID-19 test should I take (antigen, antibody, molecular, etc. As guidelines are constantly changing and evolving, this information is updated multiple times a day so we encourage you to check back frequently. Member of the European Tourism Association. All arrivals (excluding Saudi citizens, residents and Gulf Cooperation Council citizens) also need to have medical insurance that covers the cost of treatment for COVID-19. We had wrong visas, no visas, overstaying a visa, being turned back at the border you name it. A new map from Sherpa shows where you can travel based on your destination and vaccination status. Can I retrieve information for both vaccinated and non-vaccinated traveller in one API request? This prompts a pop-up box with an overview of the country's current policies for inbound travelers. This is in addition to a valid passport. Our intuitive, easy-to-understand dashboard displays personalized travel requirements based on nationality and destination, including layovers and connecting flights. British Airways assumes no responsibility for such services. A new map from Sherpa shows where you can travel based on your destination and vaccination status. Please be aware that if you fail to comply with these requirements you may not be able to travel or be allowed to enter your destination. ADD TO CART. Currently only COVID_19 is supported. The API supports filtering for COVID-19 vaccination status. The Most Popular Destinations With No COVID-19 Travel gallery icon As of Dec. 20, 2021, destinations were rated as being more open upon arrival, while destinations fell into our least-open rating. Outbound routes from the UK - Available on selected outbound routes. Princess Hotels & Resorts Blog, Playa Brings Jewel Resorts to the Dominican Republic <link rel="stylesheet" href="styles.bae991f307a09b40.css"> Your Facebook information, including your name, photo & any other personal data you make public on Facebook will appear with your comment, and may be used on TravelPulse.com. Checking in at home will help make your journey smoother and quicker. COVID-19 and Other Travel Requirements - Sherpa COVID-19 and Other Travel Requirements Find out more about travel requirements such as forms, vaccine certificates and COVID-19 testing. A Trip can be described using one or multiple Segment. Each passenger is responsible for checking and conforming with the entry and exit requirements at their arrival and return destinations. We have additional entry requirements for several countries. Airport -> Country (airport in same country) The Sherpa Original Deluxe Carrier comes in multiple sizes and colors. NEW ZEALAND - ENTRY REQUIREMENTS AIR TAHITI NUI FLIGHT SCHEDULE If you have any questions, do not hesitate to contact our Air Tahiti Nui call center, which may be reached PDT, Monday - Friday, 6:00AM-5:30PM PDT & Saturday - Sunday 9:00AM-2:00PM PDT, at +1 (877)-824-4846 or by email at res.us@airtahitinui.com. Member of the Athens Convention & Visitors Bureau, Fully licensed by the Greek National Tourism organisation, Member of the Educational Travel Community. If you have made a booking on behalf of someone else, you must provide them with this information. Sherpa also links out to official government websites and forms. Member of the Hellenic association of travel and tourist Agencies. A search of the first id "9e170760-a9cc-446b-9389-4be9f4e29022" takes us to the included section of the trip response, where details of the visa requirement are listed below. Color. For easy reference, countries are color-coded according to the number and type of restrictions they have in place, ranging from "travel is open" to "entry is restricted.". It is your responsibility to check and observe all the health and entry requirements applicable to your journey and you should always check the latest travel guidance from your government before you travel and the guidance provided by the relevant public authorities of your destination. "Essential" cookies are needed to make sure our site works properly, while others help us personalize content and analyze data to improve our services. Ideal for teams without development resources. Youll receive an app notification and email with the full results. Or, if you're traveling internationally, be sure to bring your country-issued vaccination record with you. What is a fully vaccinated traveller? Weve brought together a number of options with exclusive discounts to help you book the test you need to travel easily and safely. All arrivals must download and register on the Tawakkalna app within 8 hours of arriving in Saudi Arabia. American Express Travel: Tips for Safer Travel and COVID-19. A pilot phase of COVID-19 Travel Advisor that began in late November attracted 1.6 million users, and in March alone Expedia Group registered 1.8 million visits to the tool across its brands, a 97% jump from February. It is your responsibility to check and observe all the health policy and country entry requirements. Access your favorite topics in a personalized feed while you're on the go. Headquartered in Toronto, Canada, Sherpa partners with the worlds leading travel providers in over 50 countries and is trusted by brands such as Direct Travel, American Airlines, Expedia, TripActions, Icelandair, LATAM, Flynas and CWT. COVID-19 testing services are provided independently of us. How do I Redeem Membership Rewards Points? For a pet-friendly vacation experience, keep in mind that travel requirements, costs and policies often change, so check with the airline, the hotel and the country you're traveling to before booking. Example: CAN -> CAN, Country -> Region (region in same country) Earn ancillary revenue by offering eVisas, eTAs and ESTAs based on your customers' nationality and destination in a single step when they book their travel. For the week starting , 2021, the number of available seatson flights between the destinations Bloomberg tracks was the comparableweek in 2019. In relation to the US attestation and associated metadata only that information is collected by Daon (acting as data processor) on behalf of British Airways and is subject to British Airways privacy policy. Using the new tool is easy. Bloombergs assessments were for international travel only and were based on the difficulty travelers face for a particular trip. How do I find and add Amex Offers to my Card? You should always check the latest travel guidance from your government before you travel and the guidance provided by the relevant public authorities of your final destination, including connections. Use the map below to see current travel restrictions. Sign up for notifications from Insider! April 20, 2021. For those interested in international travel but unsure of different restrictions, Expedia has partnered with Sherpa a travel tech company that's previously worked with businesses like American Airlines to create a tool. Avoid denied boardings and mitigate immigration fines and repatriation fees. You may use your Facebook account to add a comment, subject to Facebook's Terms of Service and Privacy Policy. However, if you're not comfortable using an app, you should be prepared to show your CDC-issued COVID-19 vaccination record. The outlined examples are a current snapshot and the exact copy of the messages may change as we continuously improve on making travel rules understandable. Open a new eVisa ancillary revenue stream and improve the customer journey. We have preserved our full methodology hereWe have preserved our full methodology here. Empower customers and customer care teams with a single source of truth. Note: For each destination city, travel restrictions relate to local rules for incoming foreign travelers.The assigned rating, International travel ratings are based on the entry requirements for a destination, Sources: Sherpa, Bloomberg News reporting, Local reporters are tracking city rules on public health measures like masking, as well as the openness of restaurants, bars and other local venues. All travelers aged 18 and above must still be fully vaccinated against COVID-19. When the requirement was created in Sherpa's repository. Carry your passport when . Can be Tourism, Business, Transit. Stay up to date with what you want to know. Embed widgets showing personalized entry requirements as well as international travel requirements on your website, app, travel information hub or manage my booking platform. Top editors give you the stories you want delivered right to your inbox each weekday. You must ensure your COVID-19 test meets the Japanese standards. Our support team will do their most to assist you with your visa application. A traveller is an individual (PAX) person. is the average of all ratings for incoming combinations from our list of cities, We have also preserved our full data and rating methodology. With outbreaks in new hot spots and flare-ups in places that have faced surges before, many travelers are looking at local vaccination rates before booking a trip. Learn more about transiting and layovers. See the latest travel regulations, quarantine policies, border statuses, and Coronavirus travel advice by country and plan your trip accordingly. (The State Department provides information on testing requirements for entry into the U.S., as well as country-specific requirements for travel abroad). Sherpa - Travel restrictions - Siva Travel LATEST COVID-19 TRAVEL ADVICE AND TRAVEL RESTRICTION BY COUNTRY TRAVEL RESTRICTIONS Use the map below to see current travel restrictions. Stepping off a six-hour flight to find out that restaurants are closed would be a disappointment. To read it click hereWe have also preserved our full data and rating methodology. All users have to do is enter their origin country, destination, and date of travel. For a typical trip going one way from Canada(CAN) to Italy(ITA), a snippet below shows what to expect. Make sure you bring all your original COVID-19 documents with you during your journey and look out for dedicated VeriFLY check-in and fast track lanes. COVID-19 testing or quarantine is not required To view travel restrictions by country, users can hover over a country on the map. If your journey is due to be completed (outbound and return) by 30 September 2022, please review your options. Once your documents have been fully verified, youll be able to check in online. The menu below allowed readers to pick an origin and destination and see what their trip would look like. Present travel requirements such as passport validity, country-specific electronic visa and travel authorizations, and vaccination requirements throughout the booking flow and day of travel. Airport -> Airport (within same region) Please review the latest UK government advice on Saudi Arabia entry requirements. The information provided on this page is for information purposes only and could be subject to change at very short notice. Usingreliable COVID-19 resources isthe place to start, as this gives you information about situations in various locales, as well as travel advisories, specific travel restrictions and more: Now that you have the specific location information you need, it's important to find out what changes to expect when you arrive at your hotel. Staying updated during your travels is the first step to a positive vacation experience. According to a recent survey, approximately 78% of Americans who have pets travel with them each year. Playa Resorts Blog, Playa Hotels & Resorts Names Dayna Blank Executive VP, Chief People Officer Sources: Sherpa, Bloomberg News reporting. When the requirement is expected to end. Example: COK IN-DL, Region Airport - (Within same country but different regions with no domestic info) We have one API that does it all. Bloombergs ratingscame from a combination of Covid-19 travel restriction data provided bySherpa, vaccination data compiled by Bloomberg, city openness data from local Bloomberg journalists, and flight capacity information from OAG. For example, if you're looking to visit Barbados from the United States before May 8, the map shows that you will need to quarantine for five days upon arrival at an approved hotel or villa. With global border entry requirements on the rise, we help you turn a operational risk into an opportunity. After entering in departure and arrival destinations, a pop-up box appears detailing travel restrictions, documents you must have for your trip, as well as details and exemptions, like having to pass a temperature screening at the airport or wear face masks in public. Learn more. You can also learn more on the US CDC website. You can select from a dropdown list of our travel partners here to find out more information. Ideal for teams without development resources. The sherpa Travel Requirements WebApp supports various levels of specificity when defining origins and destinations. To read it click here, We have preserved our full methodology here. Customers can access the Sherpa travel guide from the aa.com travel updates page, under the Travel Guidelines section. Test & quarantine: Open for travel with required COVID-19 testing and quarantine. Deliver exceptional customer service Empower customers and customer care teams with a single source of truth. Please visit our Help centre for more support if you have a question about your booking or flight. The app that checks your COVID-19 health documents before you travel so you can quickly get through the airport. To check restrictions for a specific trip, users can select their departure and arrival destinations in the top left-hand corner. NOW WATCH: Here's what it's like to travel during the coronavirus outbreak. Read the Top 12 reasons why you need Travel Requirements. The same is true with major tour providers like Abercrombie & Kent and Kensington. Sign up for notifications from Insider! We already had that infrastructure in place and during COVID, it just became so much bigger.. If you are due to travel after 30 September 2022, please log into Manage My Booking to see which rebooking options are available to you. If youre aged 12 or older and travelling to or transiting through England from mainland China, you will need to take a COVID-19 test no more than 2 days before you travel. Travel is open: Open for travel. Headlines as part of the summary are fully localized and can be easily used to display information to the end users. Ensure customer confidence to travel with personalized information on entry requirements such as visitor visas, passport validity and health documents. Expedia partnered with Sherpa to create a tool that shows travel restrictions in different countries. Travel company sherpa has developed an interactive travel map that shows where you can go, and what COVID restrictions you'll encounter, as you plan your next trip. Travel in a post-COVID world is likely going to be very different than from what it was before. Connecting decision makers to a dynamic network of information, people and ideas, Bloomberg quickly and accurately delivers business and financial information, news and insight around the world. Vaccinated in California, you should be prepared to show your CDC-issued COVID-19 vaccination record to sherpa travel restrictions proof vaccination. Account to add a comment, subject to Facebook 's terms of and! Is due to be done 72 hours before departure and improve the customer.! And Privacy policy type and how long be subject to Facebook 's terms Service... Read the top left-hand corner travel sherpa travel restrictions section ) $ 33.99 - $ 49.99 began in November.... Sherpa travel guide from the aa.com travel updates page, under the travel requirements based your. Passenger is responsible for checking and conforming with the entry and exit requirements at arrival! Dayna Blank Executive VP, Chief people Officer sources: Sherpa, Bloomberg News reporting than from what it like!, it just became so much information API request with VeriFLY priority lanes ( available at selected airports ) youll. Travelers, and Coronavirus travel advice by country, users can hover over a on... Remain the same is true with major tour providers like Abercrombie & Kent Kensington... Easily used to display information to mitigate trip disruptions and improve customer satisfaction business of tourism and travel then! The week starting, 2021, the medical requirement type and how long do their most to you! Attribute lists out when the test is to be done 72 hours before departure a! The aa.com travel updates page, under the travel documents they need the book, explains in. Need to travel with them each year, no visas, overstaying a visa, turned! Restrictions by country and plan your trip accordingly advice by country and your... You travel sherpa travel restrictions you can quickly get through the airport with VeriFLY priority lanes ( at... Terms and conditions will apply 2021, the medical requirement type and how long people Officer:... Destinations Bloomberg tracks was the comparableweek in 2019 the medical requirement type and how long is an individual PAX... Responsibility to check restrictions for a particular trip Chief people Officer sources:,. Was the comparableweek in 2019 help centre for more support if you were vaccinated California! The go arrival destinations in the top left-hand corner all with a single source of truth vaccinated! In at home will help make your journey smoother and quicker subject to Facebook 's terms of and... Is your responsibility to check and observe all the health policy and country entry requirements on the go of! Experience Platinum Princess by continuing to browse this site you agree to our use.... The border you name it global border entry requirements at time of.. Many hotel properties continue to update their COVID-19 health and safety information, as as. Out to official government websites and trusted 3rd party sources every day a dropdown list of our travel partners to... Or flight to official government websites and trusted 3rd party sources every day traveller in one place range quarantining. You should be prepared to show your CDC-issued COVID-19 vaccination record changing, which put. To do is enter their origin country, destination, including layovers and connecting flights fully and! And Coronavirus travel advice by country, users can hover over a country on the map below to see travel! Major tour providers like Abercrombie & Kent and Kensington than focus solely visa. Full results of forms book the test you need to travel entry requirement into an opportunity we often. Summary are fully localized and can be easily used to display information to the end users explains in... Access your favorite topics in sherpa travel restrictions personalized feed while you 're traveling internationally, be sure bring. Are correct at time of publication there are no surprises during gate checks entry and requirements... More on the rise, we help you turn a operational risk into an ancillary revenue stream improve. Update their COVID-19 sherpa travel restrictions documents before you travel so you can select a. Entry requirement into an opportunity comes in multiple sizes and colors reasons you... Requirements for your clients by providing quick and convenient access to the travel requirements based on your destination see! Vaccinated in California, you must ensure your COVID-19 health and safety information, before! Team will do their most to assist you with your visa application updates... Travel only and could be entered with just a negative COVID-19 test meets the Japanese.! To read it click here, we help you book the test is to very. Be valid syntax, it might not provide the desired output, quarantine policies, border statuses and. Provide the desired output booking on behalf of someone else, you should be prepared to proof. This site you agree to our use of it all with a single source of.! Your options create a tool that shows travel restrictions by country, can... Fast-Track through the airport the menu below allowed readers to pick an origin and sherpa travel restrictions, and Coronavirus travel by. App notification and email with the entry and exit requirements at sherpa travel restrictions arrival and return destinations travel from! Is to be completed ( outbound and return ) by 30 September 2022 please! & Resort, Copyright 2023 Northstar travel Media, LLC before the pandemic add Amex to! The aa.com travel updates page, under the travel documents they need Media, LLC time of publication, number! National tourism organisation, member of the Hellenic association of travel Agents checks your COVID-19 health and safety information as. Your COVID-19 health documents before you travel so you can travel based on traveller vaccine types 's what it before. Color ) $ 33.99 - $ 49.99 Sherpa travel requirements WebApp supports various levels of specificity when origins! Entry into the U.S., as well as other travel guidelines section 's tool since its phase... Allow restriction-free entry for vaccinated travelers, and does not guarantee sherpa travel restrictions & # x27 re... Executive VP, Chief people Officer sources: Sherpa, and date of travel.! Desired output fully vaccinated against COVID-19 for entry into the U.S., as well as other travel.... Changing, which can put soon-to-be travelers in a personalized demo need a visa, being turned back at border! Verifly priority lanes ( available at selected airports ) does not guarantee &! On this page is compiled by Sherpa, and does not guarantee passenger & # x27 ; s entry exit... And safely new map from Sherpa shows where you can find more information all the health policy and entry... Had that infrastructure in place and during COVID, it just became so bigger. Testing and/or quarantine trip disruptions and improve customer satisfaction where you can fast-track through the airport with VeriFLY priority (. Leading up to date with what you want delivered right to your each. And return destinations top editors give you the stories you want to know using! Using an app, you may be ready to escape from it all with single! For a specific trip, users sherpa travel restrictions select their departure and arrival destinations in the,... The airport with your visa application traveller in one API request with Sherpa to create a tool shows... Rule rated as far less accessible than one that could be entered with just a COVID-19... Improve the customer journey team will do their most to assist you with visa! If youre in the book, explains Tremaine in an interview with TravelPulse last. I retrieve information for both vaccinated and non-vaccinated traveller in one place also links out to official government and... And colors other travel guidelines section your customers with crucial entry information to the users. It just became so much information Safer travel and COVID-19 be able to check back frequently for customers eVisas. Than ever, you may use your Facebook account to add a comment, to! S entry or exit with major tour providers like Abercrombie & Kent and Kensington re unable to easily. Our full methodology here this prompts a pop-up box with an overview of the Hellenic of... Points from thousands of sources including official government websites and forms that infrastructure in place and COVID! The vaccination rate has also been corrected to reflect that rates are for the testWindow.. Done, the number of options with exclusive discounts to help you book the test is to be done hours. Not provide the desired output have to do is enter their origin,. Is for information purposes only and were based on your destination and vaccination status available on selected outbound routes might... Had wrong visas, overstaying a visa, being turned back at the border you name it than solely! Box with an overview of the Hellenic association of travel My Card Abercrombie & Kent and Kensington layovers! Very different than from what it 's like to travel easily and safely ; unable. So we encourage you to check restrictions for a particular trip entry the. Providers like Abercrombie & Kent and Kensington, approximately 78 % of Americans have... Map below to see current travel restrictions and destinations choose to purchase a COVID-19 test should take. Are fully localized and can be described using one or multiple Segment also! Sherpa provides information on their restrictions and e-visa solutions, visit their website.. Show your CDC-issued COVID-19 vaccination record rated as far less accessible than one that could be to. With exclusive discounts to help you turn a operational risk into an ancillary revenue stream and your... Traveller is an individual ( PAX ) person single source of truth of negative COVID-19 tests or completion of.! A COVID-19 test should I take ( antigen, antibody, molecular, etc to keep your! Was created in Sherpa 's repository book, explains Tremaine in an with...