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Proof by Case Distinction

Proposition: For proving with knowledge K the goal G, it suffices to prove G with additional knowledge F and to prove G with additional knowledge ~F (for some formula F).

K
G
~~>
K union {F}
G
K union {~F}
G

We have to prove G.

  1. Assume F. Then ...(proof of G with additional knowledge F).
  2. Assume ~F. Then ...(proof of G with additional knowledge ~F).

Decompose the universe of situations by an assumption.


Author: Wolfgang Schreiner
Last Modification: November 30, 1999

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