Used simplifier rules: ⊦ key ∈ ri \ ks ↔ key ∈ ri ∧ ¬ key ∈ ks; (ws)% ⊦ ¬ key ∈ ks → (ri \ ks)[key] = ri[key]; (s)%key ∈ ri ⊦ ri[key] ∈ ri; (s)