27.04.2015 Views

Computability and Logic

Computability and Logic

Computability and Logic

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

PROBLEMS 125<br />

10.14 Show that the following pairs are equivalent:<br />

(a) ∀xF(x)&∀yG(y) <strong>and</strong> ∀u(F(u)&G(u)).<br />

(b) ∀xF(x) ∨∀yG(y) <strong>and</strong> ∀u∀v(F(u) ∨ G(v)).<br />

(c) ∃xF(x)&∃yG(y) <strong>and</strong> ∃u∃v(F(u)&G(v)).<br />

(d) ∃xF(x) ∨∃yG(y) <strong>and</strong> ∃u(F(u) ∨ G(u)).<br />

[In (a), it is to be understood that u may be a variable not occurring free in<br />

∀xF(x) or∀yG(y); in particular, if x <strong>and</strong> y are the same variable, u may be<br />

that same variable. In (b) it is to be understood that u <strong>and</strong> v may be any distinct<br />

variables not occurring free in ∀xF(x) ∨∀yG(y); in particular, if x does not<br />

occur in free in ∀yG(y) <strong>and</strong> y does not occur free in ∀xF(x), then u may be<br />

x <strong>and</strong> y may be v. Analogously for (d) <strong>and</strong> (c).]

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!