Algebraic Mayer–Vietoris theorem over preabelian categories

The famous “algebraic Mayer–Vietoris theorem” is usually stated for complexes over an abelian category. In the present paper this theorem is generalized for complexes over a preabelian category. We use the technique and results from the relative homological algebra that is developed in the paper (A. I. Generalov, Algebra i analyz 4, No. 3 (1992)).