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Instead of proving (**exists** `x`: `G`), we assume
(~**exists** `x`: `G`), i.e.,
(**forall** `x`: ~`G`) and deriving a contradiction:

~~>

Kexistsx:G.

Kunion {forallx: ~G}F(alse)

"We prove (**exists** `x`: `G`). Assume
(**forall** `x`: ~`G`). Then ...
(derivation of a contradiction with additional knowledge
(**forall** `x`: ~`G`))."

*We will see later how to work with universal formulas in knowledge.*

Author: Wolfgang Schreiner

Last Modification: November 30, 1999