I defined the Scheme procedure to return another procedure with 2 parameters : (define (smooth f) (?(x dx)(/ (+ (f (- x dx)) (f x) (f (+ x dx))) 3.0))) if i run this procedure with sin procedure with 2 arguments 10 and 0.0001 then it is ok ((smooth sin) 10 0.0001) ==> -0.544021109075966 if i run this procedure recursively, then it has error ((smooth (smooth sin)) 10 0.0001) ==> procedure expects 2 arguments, given 1: #<promise:temp6> So can anyone tell me where is my problem? Thank you in advance !!! PS:this is apart of exercise 1.44 in SICP