lane actor#1 "alpha" @6:11
lane actor#2 "beta" @7:11
region seq#1 seq
step ask#1 ask "a" @9:19 lane=actor#1 region=seq#1 always
step ask#2 ask "b" @10:19 lane=actor#2 region=seq#1 always
edge ask#1 -> ask#2 data always exact
