| ⊦ valid-indices(ar[n, a], nx) ↔ valid-indices(ar, nx) |
⊦ valid-indices(ar, nx) ↔ nx < # ar
⊦ nx < # ar → valid-indices(ar, nx)
Used simplifier rules: valid-indices: ⊦ valid-indices(ar, nx) ↔ nx < # ar;%valid-indices-simp: ⊦ nx < # ar → valid-indices(ar, nx);% ⊦ # ar[n, a] = # ar; (s)