Inman P. de Guzmán Manuel Ojeda-Aciego Agustín Valverde Restricted Delta-Trees in Multiple-Valued Logics. 223-232 2002 conf/aimsa/2002 AIMSA https://doi.org/10.1007/3-540-46148-5_23 db/conf/aimsa/aimsa2002.html#GuzmanOV02