c Seven variables, five clauses:
c   -x1 v x2, -x3 v x4, -x4 v -x2 v -x1 v -x7, -x5 v -x6, x6 v -x5 v -x2
c
p cnf 7 5
-1 2 0
-3 4 0
-4 -2 -1 -7 0
-5 -6 0
6 -5 -2 0