A. R. Garzon, A. del Rio
abstract:
Given a categorical crossed module H --> G, where G is a group, we show that 
the category of derivations, Der(G, H), from G into H has a natural monoidal 
structure. We introduce the Whitehead categorical group of derivations as the 
Picard category of Der(G, H) and then we characterize the invertible 
derivations, with respect to the tensor product, in this monoidal category.