Discover ambiguities or omissions i

Discover ambiguities or omissions in the following statement of requirements for part of
a ticket-issuing system:
An automated ticket-issuing system sells rail tickets. Users select their destination and
input a credit card and a personal identification number. The rail ticket is issued and their
credit card account charged. When the user presses the start button, a menu display of
potential destinations is activated, along with a message to the user to select a destination.
Once a destination has been selected, users are requested to input their credit card. Its
validity is checked and the user is then requested to input a personal identifier. When the
credit transaction has been validated, the ticket is issued.