Hyper-minimization for Deterministic Tree Automata

Hyper-minimization aims to reduce the size of the representation of a language beyond the limits imposed by classical minimization. To this end, the hyper-minimal representation can represent a language that has a finite difference to the original language. The first hyperminimization algorithm is presented for (bottom-up) deterministic tree automata, which represent the recognizable tree languages. It runs in time O(`mn), where ` is the maximal rank of the input symbols, m is the number of transitions, and n is the number of states of the input tree automaton.