- #1
roadrunner
- 103
- 0
use of quantifiers
a) Let P(x), Q(x) be open statements in the variable x with a given universe. prove that
AxP(x)\/AxQ(x)=>Ax[P(x)\/Q(x)]
[that is, prove that if the statement AxP(x)\/AxQ(x) is true then Ax[P(x)\/Q(x)] is true.
b) find a counter example for the converse in part a, that is, find an open statement for P(x) and Q(x) and a universe such that Ax[P(x)\/Q(x)] is true while AxP(x)\/AxQ(x) is false
(i will use \/ for "or", /\ for "and", Ax for "all x in a universe", Ex for (some x in a universe) )
no idea how to start rreally...
for a i thought maybe
AxP(x)\/AxQ(x)
P(c)\/Q(c)
therefore Ax[P(x)\/Q(x)]
but i totaly think that is a lame wrong asnwer haha
and even if that's correct i have NO idea how to do b...as far as I am concerned they are the same?!
Homework Statement
a) Let P(x), Q(x) be open statements in the variable x with a given universe. prove that
AxP(x)\/AxQ(x)=>Ax[P(x)\/Q(x)]
[that is, prove that if the statement AxP(x)\/AxQ(x) is true then Ax[P(x)\/Q(x)] is true.
b) find a counter example for the converse in part a, that is, find an open statement for P(x) and Q(x) and a universe such that Ax[P(x)\/Q(x)] is true while AxP(x)\/AxQ(x) is false
Homework Equations
(i will use \/ for "or", /\ for "and", Ax for "all x in a universe", Ex for (some x in a universe) )
The Attempt at a Solution
no idea how to start rreally...
for a i thought maybe
AxP(x)\/AxQ(x)
P(c)\/Q(c)
therefore Ax[P(x)\/Q(x)]
but i totaly think that is a lame wrong asnwer haha
and even if that's correct i have NO idea how to do b...as far as I am concerned they are the same?!