| https://lssds.noirlab.edu/winter_school/sites/default/files/singapore-airlines-refund-policy.pdf |
| https://lssds.noirlab.edu/winter_school/sites/default/files/what-is-singapore-airlines-refund-policy.pdf |
| https://lssds.noirlab.edu/winter_school/sites/default/files/do-i-get-a-refund-if-i-cancel-my-southwest-flight.pdf |
| https://lssds.noirlab.edu/winter_school/sites/default/files/are-southwest-flights-100-refundable.pdf |
| https://lssds.noirlab.edu/winter_school/sites/default/files/what-is-the-new-flight-credit-policy-for-southwest.pdf |
