The tag has no wiki summary.

learn more… | top users | synonyms

2
votes
1answer
120 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
votes
1answer
462 views

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
votes
3answers
156 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 ...