DeriveBinaryConstructorEquality.scala

def test[LA, LB, RA, RB, F[_, _]](
    eqA: LA =:= RA,
    eqB: LB =:= RB
): (F[LA, LB] =:= F[RA, RB]) = {
  // We start from F[LA, LB] and prove equality of the "left" part.
  val step1: F[LA, LB] =:= F[RA, LB] = eqA.liftCo[F[_, LB]]

  // We start from F[RA, LB] and prove equality of the "right" part.
  val step2: F[RA, LB] =:= F[RA, RB] = eqB.liftCo[F[RA, _]]

  // Composing the two yields what we want.
  step1.andThen(step2)
}