The compress-with-another threshold of Szykuła's Figure 3 family

Abstract

We give a self-contained pair-automaton proof of the exact compress-with-another threshold of the corrected Figure 3 family from a recent survey of open problems in synchronizing automata. For every $p \geq 3$, the automaton has $n = 3p$ states and $μ(q_0) = 4p = 4n/3$. The word $(ba)^p(ab)^p$ attains this value. Two entrance potentials and an excluded region yield the lower bound, with the endpoint exception at $p = 3$ treated explicitly. A separate reset construction proves $\operatorname{rt}(A_p) \leq 3p^2 + 4p - 1$ for every parameter. Reproducible computations verify the transition and entrance identities; the all-parameter results follow from the explicit proofs.