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1answer
67 views
definition of formula validity
I read in some sources that valid formulas are tautologies (valid under every evaluation). In the others, I read that these are formulas that have conclusions true when premises are true. Are these ...
5
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1answer
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Validity of predicate logic formulas
The following predicate logic formula is invalid (i.e. not a tautology):
$\Bigl[\forall x \,\exists y {\,.\,} P(x,y)\Bigr] \implies \Bigl[\exists y \, \forall x {\,.\,} P(x,y)\Bigr]$
Which of the ...
2
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3answers
128 views
Is switching quantifiers allowed in this instance?
In Logic In Computer Science (2nd Edition - Michael Huth and Mark Ryan), exercise 2.4.12.k is the following:
For each of the formulas of predicate logic below, either find a model which
does not ...
