  Unit propagation (which is called also Boolean Constraint Propagation) has
been an important component of every modern CDCL SAT solver since the CDCL
solver was developed. In general, unit propagation is implemented by scanning
sequentially every clause over a linear watch-list. This paper presents a new
unit propagation technique called core first unit propagation. The main idea is
to prefer core clauses over non-core ones during unit propagation, trying to
generate a shorter learnt clause. Here, the core clause is defined as one with
literal block distance less than or equal to 7. Empirical results show that
core first unit propagation improves the performance of the winner of the SAT
Competition 2018, MapleLCMDistChronoBT.
