We develop two optimization techniques. flush-machine and collapsed flushing. to improve the efficiency of automatic refinement-abased verification of out-of-order (ooo) processor models. Refinement is a notion of equivalence that can be used to check that an ooo processor correctly implements all behaviors of its instruction set architecture (ISA). https://www.roneverhart.com/5-15P-ANGLE-PLUG-B-W-HUBBELL-HBL5266CA/