evensublist([],[]).
evensublist([X],[X]).
evensublist([X,_|Xs],[X|Ys]):-evensublist(Xs,Ys).

sumofoddsublist([],0).
sumofoddsublist([_],0).
sumofoddsublist([_,X|Xs],N1):-sumofoddsublist(Xs,N), N1 is X+N.

?-evensublist([0,1,2,3,4,5,6],Xs),sumofoddsublist(Xs,N).