More other functions and fix sigma-sum describe
More other functions and fix sigma-sum describe

Higher-order procedures are procedures whose return procedures

Like the derivate of a f function.

-> scheme syntax
(define derive
  (lambda (f)
    (lambda (x) (/ (- f(x + df) f(x))
                   df))))

limbocode/lisp-insights,ryukinix/lisp-insights