Substitution of logical equivalents

logic

See:

  • Stephen Cole Kleene, Mathematical logic (1967): Replacement Theorem, page 122;

  • Peter Andrews, An introduction to mathematical logic and type theory (1986): Substitutivity of Implication, page 89 and Extended Substitutivity of Implication and Equivalence, page 94;

  • Joseph Shoenfield, Mathematical Logic (1967), Equivalence Theorem, page 34.

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