Prolog - unusual cons syntax for lists

Question

I have come across an unfamiliar bit of Prolog syntax in Lee Naish\'s paper Higher-order logic programming in Prolog. Here is the first code sample from the paper:<

Answer 1

This syntax comes from NU-Prolog. See here. It's probably just the normal list functor '.'/2 redefined as an infix operator, without the need for a trailing empty list:

?- L= .(a,.(b,[])).
L = [a,b]
Yes (0.00s cpu)
?- op(500, xfy, '.').
Yes (0.00s cpu)
?- L = a.b.[].
L = [a,b]
Yes (0.00s cpu)