Lean4
/-- The binary function on the quotient by a congruence relation `c` induced by a binary function
that is constant on `c`'s equivalence classes. -/
@[to_additive /-- The binary function on the quotient by a congruence relation `c`
induced by a binary function that is constant on `c`'s equivalence classes. -/
]
protected def liftOn₂ {β} {c : Con M} (q r : c.Quotient) (f : M → M → β)
(h : ∀ a₁ a₂ b₁ b₂, c a₁ b₁ → c a₂ b₂ → f a₁ a₂ = f b₁ b₂) : β :=
Quotient.liftOn₂' q r f h