Imaginary Piece

The set of pieces defined by Matt Galla's analysis of twistability that exist outside the set of real physical pieces. This is discussed in this thread but Matt who uses a totally different analysis then Andreas. He makes no assumption of a holding point and instead looks at all possible way a piece CAN move. For example he looks at pieces that move with BOTH the L and R layers on a 3x3x3. Such pieces doesn't exist in Andreas's method. But Matt goes on to prove such pieces "MUST exist mathematically". While not immediately obvious it turns out the Imaginary Pieces are a superset of the Virtual Pieces. Andreas now prefers the term NHP for Non-Holding Point over Imaginary.