I complain for nothing:
> >> b = a.sort {|x| x[1][0] <=> x[0][0] }
> A> While current way might does the job I have to say it's 
> very ackward to me.

as Guy points out:
> b = a.sort {|x, y| y[0] <=> x[0] }
> b = a.sort {|(x1, x2), (y1, y2)| y1 <=> x1 }

So I just shut up :).

	- Aleksi