| n ≤ # ar ⊦ # ar.mapIndices(ar.indicesWhere(φ, n), f) = # ar |
⊦ valid-indices(ar, nx) → # ar.mapIndices(nx, f) = # ar
n ≤ # ar ⊦ # ar.mapIndices(ar.indicesWhere(φ, n), f) = # ar, valid-indices(ar, ar.indicesWhere(φ, n))
Used terms: f, ar.indicesWhere(φ, n), ar