[Retros] Wikipedia

[Eric Angelini]

Hello,

I've just seen there...

   http://en.wikipedia.org/wiki/Shortest_proof_game

...this sentence :

   « "SPG" here is short for "shortest proof game" and the "9.0" indicates
how many moves must be played to reach the position; 9.0 means the position
is reached after black's ninth move, 7.5 would mean the position is reached
after seven and a half moves (that is, after white's seventh move) and so
on. »

I'm confused about this 7.5 definition ; shouldn't one read instead : «
(that is, after white's eighth move) and so on. »

Regards,
É.
(unable to remember how this ?!#§% < .5 > rule works : does someone have a
mnemonic for me?)