How to generalize known results on equations over groups

Known facts about the solvability of equations over groups are considered from a more general point of view. The theorem about the solvability of unimodular equations over torsion-free groups is generalized. A special case of the generalization is a multivariable version of this theorem. For unimodular equations over torsion-free groups, an analog of Magnus' Freiheitssatz is proved, which asserts the existence of a solution exhibiting good behavior with respect to the free factors of the initial group.