1 12687dd9 2023-08-04 jrmu ;; The first three lines of this file were inserted by DrScheme. They record metadata
 2 12687dd9 2023-08-04 jrmu ;; about the language level of this file in a form that our tools can easily process.
 3 12687dd9 2023-08-04 jrmu #reader(lib "htdp-intermediate-reader.ss" "lang")((modname |21.2|) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
 4 12687dd9 2023-08-04 jrmu 
 5 12687dd9 2023-08-04 jrmu (define (selection list1 list2)
 6 12687dd9 2023-08-04 jrmu   (cond
 7 12687dd9 2023-08-04 jrmu     [(empty? list1) empty]
 8 12687dd9 2023-08-04 jrmu     [else (local ((define (equal-to-first-of-list1? a-symbol)
 9 12687dd9 2023-08-04 jrmu                     (equal? (first list1) a-symbol)))
10 12687dd9 2023-08-04 jrmu             (append (filter equal-to-first-of-list1? list2)
11 12687dd9 2023-08-04 jrmu                     (selection list2 (rest list1))))]))