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-1
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1answer
32 views

Horn clause for the following formula

Let be $$F=A\land (\neg A\lor B)\land(A\lor \neg C)\land(\neg A\lor\neg B\lor D)\land(\neg A\lor\neg B\lor\neg C)$$ a formula. Is $F$ satisfiable? Well, firstly, I've put $F$ into another form: $$...
1
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0answers
32 views

Proving the following chain of implications

I'm struggling with a proof in the text for my logic course, and I'm wondering if someone could offer a hint or some help. The question is basically as follows. Show that if the decision problem for ...
0
votes
1answer
53 views

If $F$ is valid then $F \cup \{res(C_1,C_2,A_i)\}$ is valid

I have to prove the following problem in propositional logic: Let $F$ be a set of clauses and let $F' = F \cup \{res(C_1,C_2,A_i)\}$ be the extension of $F$ by a resolvent of some clauses $C_1,C_2 \...
1
vote
2answers
41 views

Using the rules of inferences

I know the rules of inferences and logical equivalence but I cannot seem to validate this argument. I rewrote the first premise as $\neg p\vee q$ other from that I am stuck. Any help will be ...
2
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1answer
195 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
905 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
181 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 ...