From the USMS Rule book 101.2.3 breaststroke kick:

"After the start and after each turn, a single butterfly (dolphin) kick,
which must be followed by a breaststroke kick, is permitted during or at the completion of the first arm pull, following which, all movements of the legs shall be simultaneous and in the same horizontal plane without alternating movement."

Interestingly the rule allows for some variation in sequence. For the start and the turn, it does not state when the arm pull takes place.

Question: are the following sequences legal?

a. arm pull, dolphin kick, breaststroke kick
b. dolphin kick, arm pull, breaststroke kick