(defun s+ (x y)
  (cond ((numberp x)
          (cond
           ((numberp y) (+ x y))
           ((zerop x) y)
           (t (list '+ x y))))
        ((and (numberp y)
              (zerop y)) x)
        (t (list '+ x y)) ))

(defun s- (x y)
  (cond ((numberp x)
          (cond
           ((numberp y) (- x y))
           ((zerop x) y)
           (t (list '- x y))))
        ((and (numberp y)
              (zerop y)) x)
        (t (list '- x y)) ))

    ((* ?x (/ ?y ?x)) ?y)
    ((* (/ ?x ?y) ?y) ?x)
    ((/ ?x (* ?x ?y)) ?y)
    ((/ (* ?x ?y) ?y) ?x)

Contents    Page-10    Prev    Next    Page+10    Index