1 ;; The first three lines of this file were inserted by DrScheme. They record metadata
2 ;; about the language level of this file in a form that our tools can easily process.
3 #reader(lib "htdp-intermediate-reader.ss" "lang")((modname 19.1.0) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp")))))
4 (define (filter1 rel-op alon t)
5   (cond
6     [(empty? alon) empty]
7     [else (cond
8 	    [(rel-op (first alon) t) 
9 	     (cons (first alon)
10 	           (filter1 rel-op (rest alon) t))]
11 	    [else
12 	     (filter1 rel-op (rest alon) t)])]))