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Because of (G0 => G1) iff (~G1 => ~G0), it suffices to prove

G0 => G1
K union {~G1}

"We show G0 => G1. Assume ~G1. Then ...(proof of ~G0 with additional knowledge ~G1)."

Reverse the direction of the implication.

Author: Wolfgang Schreiner
Last Modification: November 30, 1999

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