(define trapez
  (lambda (f a b)
    (* (/ (+ (f a) (f b)) 2) (- b a))
  )
)

(define x1
  (lambda (a b n)
    (+ a (/ (- b a) n))
  )
)  

(define calka-tmp
  (lambda (f a b n w)
     (if (> n 1)
         (calka-tmp f 
                    (x1 a b n) 
                    b 
                    (- n 1) 
                    (+ w (trapez f a (x1 a b n)))
          )
         w
      )
  )
)

(define calka
  (lambda (f a b n)
    (calka-tmp f a b n 0)
  )
)

(display (calka (lambda (x) (* x x)) 0. 1. 100000))