| key ∈ ri ⊦ ((ri -- key0) \ datakeys(key0, ri))[key] = ri[key], key = key0, key.data? |
key ∈ ri ⊦ (ri \ datakeys(key0, ri))[key] = ri[key], key = key0, key.data?
Used simplifier rules: ⊦ key ≠ key0 → (ri -- key0)[key] = ri[key]; (s)% ⊦ (ri -- key) \ ks = (ri \ ks) -- key; (s)