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The equivalence of finite automata and regular expressions dates back to the seminal paper of Kleene on events in nerve nets and finite automata from 1956. In the present paper we tour a fragment of the literature and summarize results on upper and lower bounds on the conversion of finite automata to regular expressions and vice versa. We also briefly recall the known bounds for the removal of spontaneous transitions (ε-transitions) on non-ε-free nondeterministic devices. Moreover, we report ondoi:10.1142/s0129054115400110 fatcat:glifsfoc4jgw7cpuyxjwlwcq6a