The duality theorems for a manifold will be derived from the corresponding ones for nets and co-nets of group systems ... Of the two types of duality… - Walther Mayer

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The duality theorems for a manifold will be derived from the corresponding ones for nets and co-nets of group systems ... Of the two types of duality theorems — the and s — the first could be obtained more easily from the corresponding one for a group system and its character system ... But when applied to the Alexander type this method fails. Also in using the net and co-net theory for both types, the less complicated Poincaré theorem serves as an introduction for the Alexander theorem.