oP(o)(mk(rs, f)), ∀ r. r ∈ rs → g(r) = a ⊦ ∃ o. oP(o)(mk(rs, f))
oP(o)(mk(rs, f)), r ∈ rs, ∀ r. r ∈ rs → g(r) = a ⊦ g(r) = a