firstPair([X,X|_]).

dupList([],[]).
dupList([F|T],[F,F|R]) :- dupList(T,R).

isDuped([]).
isDuped([F,F|T]) :- isDuped(T).

isDup(L) :- dupList(_,L).

oddSize([_]).
oddSize([_|T]) :- evenSize(T).

evenSize([]).
evenSize([_|T]) :- oddSize(T).