| perm((a × d)' + ax0, ay), perm(ay, (a × d)' + ax0), unique_al(ax0), ∀ ay0. perm(ay0, ax0) ∧ perm(ax0, ay0) → unique_al(ay0) ⊦ a ∈ ax0, unique_al(ay) |
⊦ perm(p ' + ax, ax0) ↔ ¬ ¬(p ∈ ax0 ∧ perm(ax, ax0 -1l p))
a × d ∈ ay ∧ perm(ax0, ay -1l (a × d)), perm(ay, (a × d)' + ax0), unique_al(ax0), ∀ ay0. perm(ay0, ax0) ∧ perm(ax0, ay0) → unique_al(ay0) ⊦ a ∈ ax0, unique_al(ay)
Used terms: ay, ax0, a × d