a3geffen's Hints and Pointers - exclusion rule MCR

There are quite a number of manuals on the basics of how to play a game of mahjong. The amount on strategy and tactics however is limited. Mahjong Time has asked Adrie van Geffen (a3geffen) to share his views in that territory. In the year 2011 he will publish a series of articles with hints and pointers having to do with strategy of mahjong in the different styles (except American): Hong Kong (HK); European Classic (EC); Mahjong Competition Rules (MCR); Riichi Competition Rules (RCR); Taiwanese (TW). Below part 6 – exclusion rule MCR

Although it is basic what has become to know as the exclusion rule in MCR, it appears to be difficult for some to understand and for some instructors hard to explain. Some players think they should have one point more than they calculated themselves. The chat room of Mahjong Time does not suffice for explanation and not every player is able to give it. It’s quite an important rule for it could mean that you make a false mahjong being one point short for reaching the minimum of eight.

An example: B123 C456 D789 B789 EE

There is a combination making a mixed straight worth 8 points. Then you have B789 which combines with D789 for a mixed double chow and with B123 for terminal chows. You may however only make one combination count for 1 point. It’s your choice which combination, but still only one.

The trick is that you have to be able to put the sets in one row and connect them when scoring. This is one-dimensional: one straight row and a dash (‘-‘) between the scoring elements and each connection (or dash) can only be used once for counting. No overlapping or long lines. The hand above could be represented as: B123-C456-D789-B789. No link between B123 and B789. If you want that, then you get D789-C456-B123-B789, but then of course there is no link anymore between D789 and B789.

Now consider a hand like: B123 C234 D345 B456 EE.

You can form mixed shifted chows in two ways. But then you would use the link between C234-D345 twice, which is not allowed. The right ways of representing this hand is either B456-B123-C234-D345 EE or C234-D345-B456-B123 EE. Six points for mixed shifted chows and one point for short straight.

Check out the next representations of hands and see what you can make of them:

C456-B456-C123-D789 EE

B345-B345-C345 777 EE

Written by Adrie van Geffen
homepage: http://homepages.ipact.nl/~geffen