Go backward to ExamplesGo up to TopGo forward to Logic Evaluator |

For every variable `x` and formula `A`, we have

~

"Not every**forall**`x`:`A`iff**exists**`x`: ~`A``x`satisfies`A`" equals "there exists some`x`with ~`A`".~

**exists**`x`:`A`iff**forall**`x`: ~`A`"There exists some

`x`with`A`" equals "not every`x`satisfies ~`A`".

*Universal and existential quantification are dual concepts.*

Author: Wolfgang Schreiner

Last Modification: October 6, 1999