# Solution

%% This 3-place version of get_nth_element calls a four place version %% of get_nth_element which specifies that we are at the moment %% looking at the first element of the list. get_nth_element(N,InList,OutElement) :- get_nth_element(N,1,InList,OutElement). %% If we are supposed to get the Nth element (as specified by the %% first argument) and we are at the moment looking at the Nth element %% (as specified by the second argument), then we are done. We return %% the head of the current input list. get_nth_element(N,N,[Head|_Tail],Head). %% If we are supposed to get the Nth element and we are currently %% looking at the Mth element and N is still greater than M, then we %% examine the tail (cut of the head) and specify that the we are %% now looking at the M+1th element. In other words, the head of the %% tail is the M+1th element of the original list. get_nth_element(N,M,[_Head|Tail],OutElement) :- N > M, NewM is M + 1, get_nth_element(N,NewM,Tail,OutElement).