A function which will determine that if a passed in list follows an A B pattern

Question

(define fun4

 (lambda ( ls)

(cond ((null? ls ) #f)

 (cons (((eqv? \'a (car ls))) && ((eqv? \'b (cdr ls)))))

(else (pattern2 cdr ls)))))

In

Answer 1

(define fun 
  (lambda (ls)
    (cond ((null? ls) #t)
          ((and (eq? (car ls) 'a)       ; the first item is a
                (list? (cdr ls))        ; the rest of the list
                (not (null? (cdr ls)))  ; which is not null
                (eq? (cadr ls) 'b)      ; and it starts with b
                (fun (cddr ls))) #t)    ; and the rest of the expression is 
          (else #f))))                  ; also in the A B format

Running:

> (fun '(a b a b))
#t
> (fun '(a b a))
#f
> (fun '(a b))
#t
> (fun '(a))
#f
> (fun '())
#t
>