  The 32-bit hwb (hwb-n32 for short) problem is from equivalence checking that
arises in combining two circuits computing the hidden weighted bit function.
Since 2002, it remains still unsolvable in every SAT competition. This paper
focuses on solving problems such as hwb-n32. Generally speaking, modern solvers
can detect only XOR, AND, OR and ITE gates. Other non-clausal formulas
(propositional logic structures) cannot be detected. To solve the hwb-n32
problem, we extract dynamically some special propositional logic structures,
and then use a variant of DPLL-based solvers to solve the subproblem simplified
by the extracted structure information. Using the dynamic extraction technique,
we solved efficiently the hwb-n32 problem, even some of which were solved
within 3000 seconds.
