Start working on second CGT post.
Define post content.
More readable version of sum using refine.
Bring definition of sum_cg first.
Implicit arguments for game_pair_order.
Rename game_pair_order.
First draft of post.
Add includes to coqc.
Fix link to previous post.
Some tweaks in post text.
Post file.
Add reference to new post in the first one.
Merge branch 'cgt2'

Finish post on CG sums.