Polyominoes: An Unsolved Problem
Caroline Hollingsworth · Mathematics Teacher Learning and Teaching PK-12 · 1985
Although a double-six set of dominoes contains twenty-eight different dominoes, they are indistinguishable if we turn them face down. Dominoes have only one shape (fig. 1). Similarly, we can find just one monomino (fig. 2). But, beginning with trominoes, we find more than one shape. Trominoes have two shapes (fig. 3), and tet- rominoes have five (fig. 4).