c variable names are
c u 1
c v 2
c x 3
c y 4
p cnf 4 6
a 1 2 0
d 3 1 0
d 4 2 0
1 3 4 0
-1 -2 3 4 0
-1 2 3 -4 0
1 -3 -4 0
1 3 4 0
-1 -2 -3 -4 0
-1 2 -3 4 0