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+This function is developed in *The Seasoned Schemer* pp. 84-89. It accepts an atom `a` and a list `lst` and returns `lst` with the leftmost occurrence of `a`, if any, removed. Occurrences of `a` will be found no matter how deeply embedded.
+
+	#lang racket
+	
+	(define (atom? x)
+	  (and (not (pair? x)) (not (null? x))))
+	
+	(define gamma
+	  (lambda (a lst)
+	    (letrec ([aux (lambda (l k)
+	                    (cond
+	                      [(null? l) (k 'notfound)]
+	                      [(eq? (car l) a) (cdr l)]
+	                      [(atom? (car l)) (cons (car l) (aux (cdr l) k))]
+	                      ; when (car l) exists but isn't an atom, we try to remove a from (car l)
+	                      ; if we succeed we prepend the result to (cdr l) and stop
+	                      [else (let ([car2 (let/cc k2
+	                                          ; calling k2 with val will bind car2 to val and continue with the (cond ...) block below
+	                                          (aux (car l) k2))])
+	                              (cond
+	                                ; if a wasn't found in (car l) then prepend (car l) to the result of removing a from (cdr l)
+	                                [(eq? car2 'notfound) (cons (car l) (aux (cdr l) k))]
+	                                ; else a was found in (car l)
+	                                [else (cons car2 (cdr l))]))]))]
+	             [lst2 (let/cc k1
+	                     ; calling k1 with val will bind lst2 to val and continue with the (cond ...) block below
+	                     (aux lst k1))])
+	      (cond
+	        ; was no atom found in lst?
+	        [(eq? lst2 'notfound) lst]
+	        [else lst2]))))
+	
+	(gamma 'a '(((a b) ()) (c (d ())))) ; ~~> '(((b) ()) (c (d ())))
+	(gamma 'a '((() (a b) ()) (c (d ())))) ; ~~> '((() (b) ()) (c (d ())))
+	(gamma 'a '(() (() (a b) ()) (c (d ())))) ; ~~> '(() (() (b) ()) (c (d ())))
+	(gamma 'c '((() (a b) ()) (c (d ())))) ; ~~> '((() (a b) ()) ((d ())))
+	(gamma 'c '(() (() (a b) ()) (c (d ())))) ; ~~> '(() (() (a b) ()) ((d ())))
+	(gamma 'x '((() (a b) ()) (c (d ())))) ; ~~> '((() (a b) ()) (c (d ())))
+	(gamma 'x '(() (() (a b) ()) (c (d ())))) ; ~~> '(() (() (a b) ()) (c (d ())))
+