Fermion-field theory and configuration averaging

The configuration-averaging theory of Mookerjee (see abst. A38777, a43969 of 1973) using a disorder field is put here in an equivalent picture of an electron interacting with a fermion field. This provides a more physical background to the mathematically abstruse formalism and also provides a justification to the CPA and cluster cpas proposed by Bishop and Mookerjee (see abstr. A60719 of 1974).