| a × d1 ∈ ax0, unique_al(ax0), unique_al(ax0 -1l (a0 × d0)) ⊦ a0 = a, a0 × d0 = a × d, a0 ∈ ax0 -1l (a0 × d0), a ∈ ax0 -1l (a0 × d0) |
⊦ a ∈ ax ↔ (∃ d. a × d ∈ ax)
a × d1 ∈ ax0, unique_al(ax0), unique_al(ax0 -1l (a0 × d0)) ⊦ a0 = a, a0 × d0 = a × d, a0 ∈ ax0 -1l (a0 × d0), ∃ d. a × d ∈ ax0 -1l (a0 × d0)
Used terms: ax0 -1l (a0 × d0), a