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*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`).

~~>

KG

Kunion {F}G

Kunion {~F}G

We have to prove `G`.

- Assume
`F`. Then ...(proof of`G`with additional knowledge`F`). - 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