fun trap(a,b,n,F) = 
	if n<=0 orelse b-a<=0.0 then 0.0
	else
		let
			val delta = (b-a)/real(n);
			fun trap1(x,0) = 0.0
			|   trap1(x,i) = delta*(F(x)+F(x+delta))/2.0
					 + trap1(x+delta,i-1)
		in
			trap1(a,n)
		end;