little_schemer.scheme

(define lat?
  (lambda (l)
    (or (null? l) (and (atom? (car l)) (lat? (cdr l))))))

(define rember
  (lambda (a lat)
    (cond
      ((null? lat) lat)
      ((eq? a (car lat)) (cdr lat))
      (else (cons (car lat) (rember a (cdr lat)))))))

(define firsts
  (lambda (l)
    (cond
      ((null? l) `())
      (else (cons (car (car l)) (firsts (cdr l)))))))

(define insertR
  (lambda (new old lat)
    (cond
      ((null? lat) `())
      ((eq? (car lat) old) (cons (car lat) (cons new (cdr lat))))
      (else (cons (car lat) (insertR new old (cdr lat)))))))

(define insertL
  (lambda (new old lat)
    (cond
      ((null? lat) `())
      ((eq? (car lat) old) (cons new lat))
      (else (cons (car lat) (insertL new old (cdr lat)))))))

(define subst
  (lambda (new old lat)
    (cond
      ((null? lat) `())
      ((eq? (car lat) old) (cons new (cdr lat)))
      (else (cons (car lat) (insertL new old (cdr lat)))))))

(define subst2
  (lambda (new old1 old2 lat)
    (cond
      ((null? lat) `())
      ((or (eq? (car lat) old1) (eq? (car lat) old2)) (cons new (cdr lat)))
      (else (cons (car lat) (insertL new old1 old2 (cdr lat)))))))

(define multirember
  (lambda (a lat)
    (cond
      ((null? lat) `())
      ((eq? (car lat) a) (multirember a (cdr lat)))
      (else (cons (car lat) (multirember a (cdr lat)))))))

(define multiinsertR
  (lambda (new old lat)
    (cond
      ((null? lat) `())
      ((eq? (car lat) old) (cons old (cons new (multiinsertR new old (cdr lat)))))
      (else (cons (car lat) (multiinsertR new old (cdr lat)))))))