let duplicate(k,xs) =
	let rec wew(kK,xsS) =
		match (kK,xsS) with
		(_,LNil) -> LNil
		| (0,LCons(_,t)) -> wew(k,t())
		| (n,LCons(h,_)) -> LCons(h, function () -> wew(kK-1,xsS))
	in wew(k,xs);;