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According to 15 Feb letter from Wolfgang Bibel,
K. Schutte, Vollstandige Systeme Modaler und Intuitionistischer Logik,
Ergebnisse d. Mathematik Bd. 42
Springer Verlag
section 5 has a Gentzen-type formal system for both S4 and M which 
have the subformula property.  Section 20 has an extension to S5.