In a zipper formation, are the dancers in a two by eight formation or are they in merely a distorted tidal wave?
Hence, a Zipper looks like dancers occupying all the dark spaces from two rows of a chessboard.
A Zipper can easily be created from a 1xN Wave by having everyone 1/2 Press Ahead (or 1/2 Press Back).
X - X - X - X -
- X - X - X - X
Dancers may be facing any direction within the formation. Hence, a Zipper is only a Distorted Tidal Wave if the caller so indicates.