2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/124395We introduce and study the essential inputs (variables) for terms (trees) and tree automata.10 pages, 2 figures, 60th Workshop on General Algebra, June 22-25, 2000, TU DresdenComputational ComplexityDiscrete MathematicsF.1.1; F.1.2text