From Parallel Lines or applicable T-Bone 2x4s.

Out-Facing Ends and adjacent Centers (all 8) Circulate, as In-Facing Ends and adjacent Centers Split Circulate Twice.

Double Down is usually called only from Parallel Waves or Parallel Two-Faced Lines.

Parallel Waves end in Parallel Waves; Parallel Two-Faced Lines end in Facing Lines.

Cross Double Down

Out-Facing Ends and adjacent Centers CROSSOVER Circulate, as In-Facing Ends and adjacent Centers Split Circulate Twice.

Double Down is not a new call. It has been used at the C4 level for many years.

There aren't many new ideas being written any more, and most of the quarteries in recent years have been taken from the Challenge lists.