A new proof of a theorem of Mansour and Sun

We give a new proof of a theorem of Mansour and Sun by using number theory and Rothe's identity.Comment: 3 pages, to appear in European J. Combin., see also http://math.univ-lyon1.fr/~gu

Symmetric units in modular group algebras

Let p be a prime, G a locally finite p-group, K a commutative ring of characteristic p. The anti-automorphism g bar arrow pointing right g(-1) of G extends linearly to an anti-automorphism a bar arrow pointing right a* of KG. An element a of KG is called symmetric if a* = a. In this paper we answer the question: for which G and K do the symmetric units of KG form a multiplicative group