Dominoes 03-01 (reversed) pairs, and generic backsides. Dominoes Dominoes is a family of tile-based games played with rectangular "domino" tiles. Each domino is a rectangular tile with a line dividing its face into two square "ends". Each end is marked with a number of spots (also called "pips", "nips", or "dobs") or is blank. The backs of the dominoes in a set are indistinguishable, either blank or having some common design. The domino gaming pieces make up a domino set, sometimes called a "deck" or "pack". The traditional Sino-European domino set consists of 28 dominoes, featuring all combinations of spot counts
Schläfli double six the Schläfli double six is written 1230. As Schläfli showed, the double six may be constructed from any five lines "a", "a", "a", "a", "a", that are all intersected by a common line "b", but are otherwise in general position (in particular, each two lines "a" and "a" should be skew, and no four of the lines "a" should lie on a common ruled surface). For each of the five lines "a", the complementary set of four out of the five lines has two quadrisecants: "b" and a second line "b". The five lines "b", "b", "b", "b", and "b"