Before revision:  The proposed variational principle is a generalization of the well-known Hu--Washizu variational principle, and various existing methods such as smoothed finite element methods can be expressed in terms of the proposed variational principle.
After revision:  The proposed variational principle is a generalization of the well-known Hu--Washizu variational principle, so that various existing strain smoothing methods can be expressed in terms of the proposed variational principle.