Exercise 2.23 single pair of ribs で実装ときた。これって gosh> (empty-env) () gosh>で、 gosh> (extend-env '(y) '(8) (empty-env)) ((y) . (8)) gosh>で、 gosh> (extend-env '(d x) '(6 7) (exptend-env '(y) '(8) (empty-env))) ((d x y) . (6 7 8))…