v3f axis_front, axis_back, axis;
v3_cross( inf_front->dir, inf_front->n, axis_front );
v3_cross( inf_back->dir, inf_back->n, axis_back );
v3f axis_front, axis_back, axis;
v3_cross( inf_front->dir, inf_front->n, axis_front );
v3_cross( inf_back->dir, inf_back->n, axis_back );