It could be the flight booking system described in Sictus Prolog's old homepage:
SICStus Prolog is a workhorse in the transport and logistics industries, running systems that handle a third of all airline tickets, and helping railways to operate their trains better.
“Most people probably have used SICStus Prolog without knowing it,” says Mats Carlsson, its lead developer. “One of our customers runs a flight booking system on SICStus which handles nearly a third of all airline tickets in the world.”
SICStus Prolog is a workhorse in the transport and logistics industries, running systems that handle a third of all airline tickets, and helping railways to operate their trains better.
“Most people probably have used SICStus Prolog without knowing it,” says Mats Carlsson, its lead developer. “One of our customers runs a flight booking system on SICStus which handles nearly a third of all airline tickets in the world.”
https://web.archive.org/web/20190203010151/https://www.sics....
The new homepage doesn't say anything about flight bookings and I can't find anything about it in the "Customers" page either:
https://sicstus.sics.se/customers.html
I have a sneaking suspicion that might mean the customer replaced Prolog with something else, possibly some kind of machine learning :P