complement.el

(remove-if 'oddp '(1 2 3 4 5 6))
;;=>(2 4 6)

(defun complement (fn)
  (lexical-let ((fn fn))
    (lambda (&rest args) (not (apply fn args)))))

(remove-if (complement 'oddp) '(1 2 3 4 5 6))
;;=>(1 3 5)