Existence of a multiplicative basis for a finitely spaced module over an aggregate
It is proved that a finitely spaced module over $k$-category admits a multiplicative basis (such a module gives rise to a matrix problem in which the allowed column transformations are determined by a module structure, the row transformations are arbitrary, and the number of canonical matrices is finite).
English version (Springer): Ukrainian Mathematical Journal 46 (1994), no. 5, pp 604-617.
Citation Example: Roiter A. V., Sergeychuk V. V. Existence of a multiplicative basis for a finitely spaced module over an aggregate // Ukr. Mat. Zh. - 1994. - 46, № 5. - pp. 567–579.