# Logic problems

#### bubbleman

Hello there!
I have 3 tasks to solve, and I believe that I've achieved correct answer, but I might be totally wrong.

The question is if these expressions are correct or incorrect (true/false)

a) C -> (A -> B) |= -C ^ (-A v B)

b) C -> A( -> B) |= -C v -A v B

c) -C v (-A v B) |= C->(A->B)

/David.T

#### emakarov

MHF Hall of Honor
Recall that -A \/ B is equivalent to A -> B and try rewriting the formulas you are given using this equivalence as much as possible.

#### bubbleman

A = 1, B = 1, C = 1

LEFT: 1 -> (1 -> 1) gives 1 -> 1 gives 1

RIGHT: 0 ^ (0 v 1) gives 0 ^ 1 gives 0

1 =| 0 must be incorrect/false?

#### hmmmm

do you not have any proof methods e.g semantic tableau that you can use?

#### emakarov

MHF Hall of Honor
A = 1, B = 1, C = 1

LEFT: 1 -> (1 -> 1) gives 1 -> 1 gives 1

RIGHT: 0 ^ (0 v 1) gives 0 ^ 1 gives 0

1 |= 0 must be incorrect/false?
Yes.

#### hmmmm

can we not just simply draw up three tableau's for these to show if they are true or if not find a model using the tableau?