start small, simple

I'm learning Prolog as part of CS2104. Consider a predicate in Prolog that checks if the Nth-indexed element of a list is Y:

nth([],_,_) :- fail.
nth([X|_],0,X).
nth([_|T],N,Y) :- N #> 0, N1 #= N-1, nth(T,N1,Y).

This is fine ...

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