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Because of ~(`G`_{0} /\ `G`_{1}) iff
~`G`_{0} \/ ~`G`_{1}, the *indirect method*
leads to

~~>

KG_{0}/\G_{1}~~>

Kunion {~G_{0}\/ ~G_{1}}F(alse)

Kunion {~G_{0}}F(alse)

Kunion {~G_{1}}F(alse)

We have to prove `G`_{0} /\ `G`_{1}.

- Assume ~
`G`_{0}. Then ...(derivation of a contradiction.) - Assume ~
`G`_{1}. Then ...(derivation of a contradiction.)

*We will see later this technique of "case distinction".*

Author: Wolfgang Schreiner

Last Modification: November 30, 1999