enrich list-data with variables x : list; y : list; z : list; a : elem; b : elem; c : elem; m : nat; n : nat; partial functions . [ . ] : list × nat → elem with λ x, n. n < # x; comment: get is zero based; . [ . ] : list × nat × elem → list with λ x, n, a. n < # x; comment: put is zero based; axioms get-zero: (a + x)[0] = a; used for: s, ls; get-succ: (a + x)[n + 1] = x[n]; used for: s, ls; put-zero: (b + x)[0, a] = a + x; used for: s, ls; put-succ: (b + x)[n + 1, a] = b + x[n, a]; used for: s, ls; end enrich