The category of crossed complexes gives an algebraic model of CW -complexes and cellular maps. Free crossed resolutions of groups contain information on a presentation of the group as well as higher homological information. We relate this to the problem of calculating non-abelian extensions. We show how the strong properties of this category allow for the computation of free crossed resolutions...

In this paper, we construct a neat description of the passage from crossed squares of commutative algebras to 2-crossed modules analogous to that given by Conduché in the group case. We also give an analogue, for commutative algebra, of T.Porter’s [13] simplicial groups to n-cubes of groups which implies an inverse functor to Conduché’s one.

This paper is prompted by work of Grandjee an and Ladra on homol-ogy crossed modules. We deene the homology of a crossed module in dimensions one and two via the equivalence of categories with group objects in groupoids. We show that for any perfect crossed module, its second homology crossed module occurs as the kernel of its universal central extension as deened by Norrie. Our rst homology is...

Lateral medullary infarction (LMI) or Wallenberg syndrome is a type of brain stem stroke, more specifically, a type of crossed brain stem syndrome. LMI is a well-described entity with several documented typical characteristics including pain and temperature impairment in the ipsilateral to the lesion side of the face and the contralateral side of the trunk and limbs. We present a case of LMI wh...