c pigeon-1: placing 2 pigeons into 1 holes
c 
c File generated by 'pigeonhole', (c) Tjark Weber
c 
c The SAT encoding of this problem is very straightforward.  For each pigeon i
c and each hole j we have a variable x_{n*(i-1)+j} which means that pigeon i
c is placed in hole j.  Then we have n+1 clauses which say that a pigeon has
c to be placed in some hole.  Then for each hole we have a set of clauses
c ensuring that only one single pigeon is placed into that hole.
c 
c This encoding leads to a total of (n+1) * n propositional variables and
c (n+1) + n * (n * (n+1) / 2) clauses.
c 
c The resulting SAT problem is unsatisfiable.
c 
p cnf 2 3
1 0
2 0
-1 -2 0