GAUGE INVARIANCE INVARIANZA DE UN PATRON RENORMALIZACION RENORMALIZATION A renormalisation group technique for spin and gauge systems with topological excitations ESPIN SPIN TOPOLOGIA TOPOLOGY Application of a modified mean-field method to a gauge-invariant variational calculation CLUSTER MODEL DISPERSION RELATIONS ISING MODEL MEAN-FIELD THEORY METODO DE LA MATRIZ DE TRANSFERERENCIA MODELO DE ISING 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 TEORIA DEL CAMPO MEDIO TRANSFER MATRIX METHOD