| ⊦ ri |≤ key0 |≤ key1 = ri |≤ key1, key0 < key1 |
⊦ ri = ri0 ↔ (∀ key. (key ∈ ri ↔ key ∈ ri0) ∧ (key ∈ ri → ri[key] = ri0[key]))
⊦ key0 < key1, ∀ key. (key ∈ ri |≤ key0 |≤ key1 ↔ key ∈ ri |≤ key1) ∧ (key ∈ ri |≤ key0 |≤ key1 → (ri |≤ key0 |≤ key1)[key] = (ri |≤ key1)[key])
Used terms: ri |≤ key1, ri |≤ key0 |≤ key1