## ABSTRACT

Here px, py, and pz are the components of the stress vector along the boundary A. The integral on the left-hand side and the rst integral on the right-hand side are extended over the whole volume, V, of the body and the second integral on the right-hand side along the boundary A. The equation is an identity if the statical conditions are fullled and is then valid for any displacement eld satisfying the geometrical conditions. If, on the contrary, the equation is known to be valid for any displacement eld, the statical conditions are fullled.