From any formation [e.g. a wave or line] where designated dancers can Fold and others can Squeeze: Designated dancers Fold, others Squeeze [i.e. if adjacent Trade and slide apart, if apart slide together and Trade], then folders step ahead into squeezers spot.
Editors note: From any wave or line: Centers Exchange is the same as Switch the Wave/Line. From any line or wave: Ends Exchange is the same as Cross Roll to a Wave/Line. If Switch and Cross Roll always seemed sort of related, Bill's call shows you why! Note also that the action of Fold and step ahead is the same as Run.
Cross Exchange - Same as above except designated dancers Cross Fold.
From either a line or wave both ends Cross Exchange and centers Cross Exchange are the same as Mix [or everybody Cross Run].