GAUGE INVARIANCE INVARIANZA DE UN PATRON RENORMALIZACION RENORMALIZATION ESPIN ISING MODEL MEAN-FIELD THEORY METODO DE LA MATRIZ DE TRANSFERERENCIA MODELO DE ISING SPIN TEORIA DEL CAMPO MEDIO TOPOLOGIA TOPOLOGY TRANSFER MATRIX METHOD A renormalisation group technique for spin and gauge systems with topological excitations Application of a modified mean-field method to a gauge-invariant variational calculation CLUSTER MODEL DISPERSION RELATIONS NIVELES ENERGETICOS P STATES POLOS DE REGGE REGGE POLES RELACIONES DE DISPERSION Renormalisation group for the transfer matrix Structure of the p-singularity in a multicluster model