anchor.diff:         ((A 1) (if-true 'nil (if (equal (car '()) '?) 't  (memb? (cdr '())))))
          ((A) (equal-same 'nil))
          ((E A 1 1) (remb xs))
  -
          ((E A 1 1)
           (if-nest-E (atom xs)
             '()
  
positive.code:        (() (if-same (atom x) 't)))
        ((dethm ctx?/sub (x y)
           (if (ctx? x) (if (ctx? y) (equal (ctx? (sub x y)) 't) 't) 't))
  
         (star-induction y)
         (()
          (if-same (ctx? x)
  
negative.code:        ((A E A A A 1 Q) (atom/cons (sub x (car y)) (sub x (cdr y))))
         ((A E A A A 1 E Q 1) (car/cons (sub x (car y)) (sub x (cdr y))))
         ((A E A A A 1 E E 1) (cdr/cons (sub x (car y)) (sub x (cdr y))))
         ((A E A A A 1)
          (if-false (equal (cons (sub x (car y)) (sub x (cdr y))) '?)
            (if (ctx? (sub x (car y))) 't (ctx? (sub x (cdr y))))))
  