intersection (l1, l2) = let
	fun loop([], l2)  = []
	| loop(l1, []) = []
	| loop(x::xs, y::ys) = if in_list(x,y) = true then x::loop(xs,ys) else loop(x::xs,ys)

in
loop(l1,l2)
end

//What is wrong?