DESCRIPTORS: *Algebraic topology, *Alge ra, Sequences, *A LGEBRAS, Groups (Mathematics). Ad itive relations are regar d as being basic, and suitable formal axioms valid in the category of all additive relations are set up. The construction of submodules in an abelian category is quite indirect, in that the submodules must be described as equivalence classes of monomorphisms. In the category of additive relations the lattice order properties are present from the start, along with the composition properties. (Author).