Dominoes spots from one to six are generally arranged as they are on six-sided dice, but because blank ends having no spots are used, seven faces are possible, allowing 28 unique pieces in a double-six set. However, this is a relatively small number especially when playing with more than four people, so many domino sets are "extended" by introducing ends with greater numbers of spots, which increases the number of unique combinations of ends and thus of pieces. Each progressively larger set increases the maximum number of pips on an end by three, so the common extended sets are double-nine, double-12,
Dominoes of Emperor Xiaozong of Song (r. 1162–1189). Andrew Lo asserts that Zhou Mi meant dominoes when referring to "pupai", since the Ming author Lu Rong (1436–1494) explicitly defined "pupai" as dominoes (in regard to a story of a suitor who won a maiden's hand by drawing out four winning "pupai" from a set). The earliest known manual written about dominoes is the "(Manual of the Xuanhe Period)" written by Qu You (1341–1437), but some Chinese scholars believe this manual is a forgery from a later time. In the "Encyclopedia of a Myriad of Treasures", Zhang Pu (1602–1641) described the game