| ⊦ ∀ key. (key ∈ (ri \ ks0) \ ks1 ↔ key ∈ ri \ (ks0 ∪ ks1)) ∧ (key ∈ (ri \ ks0) \ ks1 → ((ri \ ks0) \ ks1)[key] = (ri \ (ks0 ∪ ks1))[key]) |
⊦ (key ∈ (ri \ ks0) \ ks1 ↔ key ∈ ri \ (ks0 ∪ ks1)) ∧ (key ∈ (ri \ ks0) \ ks1 → ((ri \ ks0) \ ks1)[key] = (ri \ (ks0 ∪ ks1))[key])