While you're at it, also add symmetry :)
What exactly do you want here? Lemma lty_bi_le_sym A1 A2 : ⊢ (A1 <: A2 ∧ A2 <: A1) *-* A1 <:> A2. ?
Lemma lty_bi_le_sym A1 A2 : ⊢ (A1 <: A2 ∧ A2 <: A1) *-* A1 <:> A2.
Or just in one direction
That's anti-symmetry, and just the the definition.
Symmetry is A1 <:> A2 -∗ A2 <:> A1.
A1 <:> A2 -∗ A2 <:> A1
Derp. Of course it is. My bad - Added!