Two men stand at a chalkboard that forms part of a stone wall in front of a number of tables and chairs of which only a few are occupied .
Chances are about even that a couple of men are writing equations on a chalkboard .
It is highly unlikely that a couple of men are writing equations on a chalkboard .
Chances are about even that a couple of men are writing equations on a chalkboard .
A couple of men are writing equations on a chalkboard .