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We show that the following is a tautology:

((A \/ B) /\  (A => C) /\  (B => C)) => C.
We assume that its truth value is false and then derive a contradiction:
((A \/ B) /\  (A => C) /\  (B => C)) => C
Because the implication is false, C is false and the conjuncts are true. Thus A and B must be false. Therefore A \/ B is false, which contradicts above derivation.
Author: Wolfgang Schreiner
Last Modification: November 30, 1999

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