| key ∈ ks ⊦ # ks = 0, key0 ∈ (ri ⊖ key) ⊖ ks ↔ key0 ∈ ri ⊖ ks, ks = ∅, (key0 ∈ (ri ⊖ key) ⊖ ks ↔ key0 ∈ ri ⊖ ks) ∧ (key0 ∈ (ri ⊖ key) ⊖ ks → ((ri ⊖ key) ⊖ ks)[key0] = (ri ⊖ ks)[key0]) |
key ∈ ks ⊦ # ks = 0, key0 ∈ (ri ⊖ key) ⊖ ks ↔ key0 ∈ ri ⊖ ks, ks = ∅