Finally AC. Yes brootforce rules here. But it's a little BIT tricky brootforce.

Edited by author 22.03.2011 12:39

"table of covering reducing"- my term(auto trans. is used)
Classical algo for minimal covering had good success in this problem
and under emotion I wrote that helping.
Again: we have NP problem but  can to speed up.
So, in stack data we add matrix of covering for example as
1 0 1 0
0 1 1 1
0 1 1 1
This means that 4 points(columns) are covered by 3 sets(rows). First point is covered by only 1-th row and we must use Set-1 as obligatory.
Thus, the search tree hasn't branching in this-time vertex and we create
only one child vertex with reduced matrix:
1 1
1 1
because 1,3 points are covered by obligated row 1.
Finally: when we   make choice for some set in search tree  we transfer in child
vertex reduced matrix.

P.S. I had expirience in this algo from boolean design(all practice problem are NP).