This game is based on Mahjong which is a four-player game that originated in China. Mahjong is played with a set of 144 tiles--not unlike playing cards--and involves both skill and luck. Winning is by points, and gambling is optional. There are both American and British versions of mahjong. The British, or English, version is very similar to the Chinese version, in that each of the four players draw and discard a tile in turn until they have formed winning groups of tiles, at which point they can call “pung” or “mahjong.”
In Shisen-Sho (aka 'Four Rivers', 'Szechuan', 'Shisen' or 'Nikakudori') the object is to remove all tiles from the field (as in 'Shanghai'). Only two matching or identical tiles can be removed at a time. The two tiles can only be removed if they can be connected with, at most, three connected lines. They must be connected by an imaginary line which does not pass through any other tile. Distance does not matter. When you remove tiles at the edges, other tiles become available for matching. These games uses what could be called the 'one-layer two-angles arcade rules'.
The number of tiles doesn't matter (as long as it has all four of the tiles used) and the layout may be different from game to game (the traditional one is a rectangular grid).
Remember that there normally are 4 of each tile - matching the "wrong" two first may make you loose the game, the game become unsolvable and you're trapped...
Szechuan is the name of an Chinese province, Shisen-Sho (or Sichuan) the Japanese name for the same area and Four Rivers is the English translation of that name. The myth is that Mahjongg is so popular in the province of Szechuan (probably true) that they created a different variant to play with the tiles (probably false).
Both the name of the original author and time of creation are unknown (probably Japanese).