def seq_at_b2
import bendtorch@1.3.0.0/main.bend as Bendtorchimport Base
857def seq_at_b2(-P1: Type, -P2: Type, -X: Type, -Y: Type, -S1: Type, ba: P1 -> S1 -> Y -> P1 -> Bwd<P1, X>, p1: P1, s1: S1, g1: P1, r: Bwd<P2, Y>) -> Bwd<Two<P1, P2>, X>:
858 match r:
859 case Bwd{p2, dy, g2}: seq_b3(P1, P2, X, p2, g2, ba(p1, s1, dy, g1))