ar1 = ar0[n, a] ⊦ # ar0 = # ar1 ∧ (∀ m. m < # ar0 → ar1[m] = (n = m ⊃ a;ar0[m]))
# ar0 = # ar1 ∧ (∀ m. m < # ar0 → ar1[m] = (n = m ⊃ a;ar0[m])) ⊦ ar1 = ar0[n, a]