Integer intervals

Uses Integers

The closed interval bracketed by two integers has sort ℤ⋯ℤ and is defined using the operator
 ℤ ⋯ ℤ : ℤ⋯ℤ

Special cases:
- ℕ ⋯ ℕ : ℕ⋯ℕ with ℕ⋯ℕ ⊆ ℤ⋯ℤ
- ℕ.nz ⋯ ℕ.nz : ℕ.nz⋯ℕ.nz with ℕ.nz⋯ℕ.nz ⊆ ℕ⋯ℕ