2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/116114We study the complexity of the model checking problem, for fixed model A, over certain fragments L of first-order logic. These are sometimes known as the expression complexities of L. We obtain various complexity classification theorems for these logics L as each ranges over models A, in the spirit of the dichotomy conjecture for the Constraint Satisfaction Problem -- which itself may be seen as the model checking problem for existential conjunctive positive first-order logic.Logic in Computer ScienceComputational Complexitytext