;; file: 2_01.rkt
;; file: 2_02.rkt
;; file: 2_03.rkt
;; file: 2_04.rkt
;; file: 2_05.rkt
;; file: 2_06.rkt
;; file: 2_07.rkt
;; file: 2_08.rkt
;; file: 2_09.rkt
;; file: 2_10.rkt
;; file: 2_11.rkt
;; file: 2_12.rkt
;; file: 2_13.rkt
;; file: 2_14.rkt
;; file: 2_15.rkt
;; file: 2_16.rkt
;; file: 2_17.rkt
;; 2_17 / 4_62 / 4_63 / 4_69
;; file: 2_18.rkt
;; file: 2_19.rkt
;; file: 2_20.rkt
;; file: 2_21.rkt
;; file: 2_22.rkt
;; file: 2_23.rkt
;; file: 2_24.rkt
;; file: 2_25.rkt
;; file: 2_26.rkt
;; file: 2_27.rkt
;; file: 2_28.rkt
;; file: 2_29.rkt
;; file: 2_30.rkt
;; file: 2_31.rkt
;; file: 2_32.rkt
;; file: 2_33.rkt
;; file: 2_34.rkt
;; file: 2_35.rkt
;; file: 2_36.rkt
;; file: 2_37.rkt
;; file: 2_38.rkt
;; file: 2_39.rkt
;; file: 2_40.rkt
;; file: 2_41.rkt
;; file: 2_42.rkt
;; 2_42 / 4_44
;; TODO
;; file: 2_43.rkt
;; file: 2_44.rkt
;; file: 2_45.rkt
;; file: 2_46.rkt
;; file: 2_47.rkt
;; file: 2_48.rkt
;; file: 2_49.rkt
;; file: 2_50.rkt
;; file: 2_51.rkt
;; file: 2_52.rkt
;; file: 2_53.rkt
;; file: 2_54.rkt
;; file: 2_55.rkt
;; file: 2_56.rkt
;; file: 2_57.rkt
;; file: 2_58.rkt
;; file: 2_59.rkt
;; file: 2_60.rkt
;; file: 2_61.rkt
;; file: 2_62.rkt
;; file: 2_63.rkt
;; file: 2_64.rkt
;; file: 2_65.rkt
;; file: 2_66.rkt
;; file: 2_67.rkt
;; file: 2_68.rkt
;; file: 2_69.rkt
;; file: 2_70.rkt
;; file: 2_71.rkt
;; file: 2_72.rkt
;; file: 2_73.rkt
;; file: 2_74.rkt
;; file: 2_75.rkt
;; file: 2_76.rkt
;; file: 2_77.rkt
;; file: 2_78.rkt
;; file: 2_79.rkt
;; file: 2_80.rkt
;; file: 2_81.rkt
;; file: 2_82.rkt
;; file: 2_83.rkt
;; file: 2_84.rkt
;; file: 2_85.rkt
;; file: 2_86.rkt
;; file: 2_87.rkt
;; file: 2_88.rkt
;; file: 2_89.rkt
;; file: 2_90.rkt
;; file: 2_91.rkt
;; file: 2_92.rkt
;; file: 2_93.rkt
;; file: 2_94.rkt
;; file: 2_95.rkt
;; file: 2_96.rkt
;; file: 2_97.rkt