Characterization Classes Defined without Equality. - Raimon Elgueta (Stud Logica, 1997)

Freeness in Classes Without Equality. - Raimon Elgueta (J. Symb. Log., 1999)

Algebraic Characterizations for Universal Fragments of Logic. - Raimon Elgueta (Math. Log. Q., 1999)

Definability of Leibniz Equality. - Raimon Elgueta; Ramon Jansana (Stud Logica, 1999)

Review of Protoalgebraic Logics by J. Czelakowski. - Raimon Elgueta (Stud Logica, 2003)