def seq_at_step
import bendtorch@1.3.0.0/main.bend as Bendtorchimport Base
865def seq_at_step(-P1: Type, -P2: Type, sa: Opt -> P1 -> P1 -> OptState<P1> -> Step<P1>, sb: Opt -> P2 -> P2 -> OptState<P2> -> Step<P2>, +op: Opt, p: Two<P1, P2>, g: Two<P1, P2>, st: Two<OptState<P1>, OptState<P2>>) -> Step<Two<P1, P2>>:
866 match p g st:
867 case Two{p1, p2} Two{g1, g2} Two{s1, s2}: pair_s3(P1, P2, sa(op, p1, g1, s1), sb(op, p2, g2, s2))