  The relations between solutions of the three types of totally linear partial
differential equations of first order are presented. The approach is based on
factorization of a non-homogeneous first order differential operator to
products consisting of a scalar function, a homogeneous first order
differential operator and the reciprocal of the scalar function. The
factorization procedure is utilized to show that all totally linear
differential equations of first order can be transformed to each other, and in
particular to a homogeneous one.
