if true t e t if false t e e member x nil false member x cons y ys if eq x y true member x ys eq nil nil true eq O x 0 y eq x y eq 0 x 1 y false eq 1 x 0 y false eq 1 x 1 y eq x y negate 0 x 1 x negate 1 x 0 x choice cons x xs x choice cons x xs choice xs guess nil nil guess cons clause cnf cons choice clause guess cnf verify nil true verify cons l ls if member negate l ls false verify ls sat cnf satck cnf guess cnf satck cnf assign if verify assign assign unsat 2.2 choice cons x xs choice xs verify cons l ls negate l member x cons y ys eq x y satck cnf assign verify assign guess cons clause cnf guess cnf member x cons y ys if eq x y true member x ys member x cons y ys member x ys verify cons l ls verify ls guess cons clause cnf choice clause verify cons l ls member negate l ls sat cnf guess cnf eq 1 x 1 y eq x y eq O x 0 y eq x y satck cnf assign if verify assign assign unsat sat cnf satck cnf guess cnf verify cons l ls if member negate l ls false verify ls true sat cnf satck cnf guess cnf false satck cnf assign if verify assign assign unsat false sat cnf guess cnf false guess cons clause cnf guess cnf true choice 1 0 verify 1 0 negate 1 0 1 1 0 sat 1 0 unsat 0 0 guess 1 1 0 negate 1 0 choice 1 0 member 2 0 eq 2 0 false 0 0 satck 2 0 O 1 0 true 0 0 sat 1 0 eq 2 0 satck 2 0 if 3 0 0 1 0 nil 0 0 guess 1 0 cons 2 2 1 member 2 0 if 3 0 verify 1 0 satck cnf assign verify assign false guess cons clause cnf choice clause false verify cons l ls verify ls true choice 1 0 verify 1 0 negate 1 0 1 1 0 sat 1 0 unsat 0 0 guess 1 0 negate 1 0 choice 1 0 member 2 0 eq 2 0 false 0 0 satck 2 0 O 1 0 true 0 0 sat 1 0 eq 2 0 satck 2 0 if 3 0 0 1 0 nil 0 0 guess 1 0 cons 2 2 1 member 2 0 if 3 0 verify 1 1 0 verify cons l ls if member negate l ls false verify ls false verify cons l ls member negate l ls false member x cons y ys member x ys true choice 1 0 verify 1 0 negate 1 0 1 1 0 sat 1 0 unsat 0 0 guess 1 0 negate 1 0 choice 1 0 member 2 0 eq 2 0 false 0 0 satck 2 0 O 1 0 true 0 0 sat 1 0 eq 2 0 satck 2 0 if 3 0 0 1 0 nil 0 0 guess 1 0 cons 2 2 1 member 2 2 0 if 3 0 verify 1 0 member x cons y ys if eq x y true member x ys false member x cons y ys eq x y false eq O x 0 y eq x y eq 1 x 1 y eq x y true choice 1 0 verify 1 0 negate 1 0 1 1 1 1 sat 1 0 unsat 0 0 guess 1 0 negate 1 0 choice 1 0 member 2 0 eq 2 0 false 0 0 satck 2 0 O 1 1 true 0 0 sat 1 0 eq 2 2 0 satck 2 0 if 3 0 0 1 1 1 nil 0 0 guess 1 0 cons 2 1 member 2 0 if 3 0 verify 1 0 verify cons l ls negate l false choice cons x xs choice xs true choice 1 1 0 verify 1 0 negate 1 0 1 1 1 sat 1 0 unsat 0 0 guess 1 0 negate 1 0 choice 1 0 member 2 0 eq 2 0 false 0 0 satck 2 0 O 1 1 true 0 0 sat 1 0 eq 2 0 satck 2 0 if 3 0 0 1 1 nil 0 0 guess 1 0 cons 2 2 1 member 2 0 if 3 0 verify 1 0 NaTT certifiable-1.6