Self-dual primitives for modal logic

This publication has 2 references indexed in Scilit:

• Conditioned Disjunction as a primitive connective for them-valued Propositional Calculus
  Mathematische Annalen, 1951
• Symbolic Logic. By C.I. Lewis and C.H. Langford. Pp. xi 506. 21s. 1932. (The Century Company, New York and London)
  The Mathematical Gazette, 1934