key ∈ kx, ∀ key0. key0 ∈ kx → key0 ∈ ri ⊦ key ∈ ri
Used simplifier rules: ⊦ key ∈ dom ri ↔ key ∈ ri; (s)% ⊦ key ∈ kx.toSet ↔ key ∈ kx; (s)