mk(rs, f) = ∅, ∀ r. r ∈ rs → g(r) = a ⊦ mk(rs, f, g) = ∅
mk(rs, f, g) = ∅ ⊦ mk(rs, f) = ∅ ∧ (∀ r. r ∈ rs → g(r) = a)