[1] BREZZI, HAGER, HAVIART: Error estimates of the finite element solution ef variational inequalities. Part I: Primal methods; Part II: Mixed methods. preprint of the University Paris VI, 1976.

[2] CÉA J.: Optimisation. théorie et algorithmes, Paris, Dunod, 1971. MR 0298892

[3] CIARLET P. G., RAVIART P. A.: General Lagrange and Hermite interpolation in $R^n$ with applications to finite element methods. Arch. Rational Mech. Anal. 46 (1972), 177-199. MR 0336957

[4] HASLINGER J., HLAVÁČEK I.: Contact between elastic bodies. (to appear).

[5] HLAVÁČEK I.: Dual finite element analysis for unilateral boundary value problems. Apl. Mat. 22 (1977), 1-51. MR 0426453

[6] NEČAS J.: Les méthodes directes en théorie des équations elliptiques. Praha, Academia, 1967. MR 0227584

[7] NEČAS J., JARUŠEK J., HASLINGER J.: On the solution of the variational inequality of the Signorini problem with friction. (to appear).

[8] THOMAS J.: Sur l'analyse numéique des méthodes d'elements finis hybrides et mixtes. Thèse 1977, Université de Paris VI.