| key ∈ keys(fs, ax0) ↔ (∃ adr. adr ∈ ax0 ∧ fs[adr].key = key), ∀ key, fs. key ∈ keys(fs, ax0) ↔ (∃ adr. adr ∈ ax0 ∧ fs[adr].key = key), ∃ adr0. (adr0 = adr ∨ adr0 ∈ ax0) ∧ fs[adr0].key = key ⊦ key = fs[adr].key, key ∈ keys(fs, ax0) |
adr0 ∈ ax0, ∀ key, fs. key ∈ keys(fs, ax0) ↔ (∃ adr. adr ∈ ax0 ∧ fs[adr].key = key) ⊦ fs[adr0].key = fs[adr].key, fs[adr0].key ∈ keys(fs, ax0), ∃ adr. adr ∈ ax0 ∧ fs[adr].key = fs[adr0].key