  We introduce a procedure for proving safety properties. This procedure is
based on a technique called Partial Quantifier Elimination (PQE). In contrast
to complete quantifier elimination, in PQE, only a part of the formula is taken
out of the scope of quantifiers. So, PQE can be dramatically more efficient
than complete quantifier elimination. The appeal of our procedure is twofold.
First, it can prove a property without generating an inductive invariant.
Second, it employs depth-first search and so can be used to find deep bugs.
