# Why is this truth table incorrect?

## Homework Statement

Create a truth table for ((P->Q) == (Q->P))

## The Attempt at a Solution

I've had two quizes with problems just like this marked wrong in my college logic course. I confronted the professor about it and he just told me to study the truth tables. I'm very confused as to why this is wrong, because I've taken a discreet math course previously.

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Dick
Homework Helper
I don't think it is wrong. Looks perfectly fine to me.

## Homework Statement

Create a truth table for ((P->Q) == (Q->P))

## The Attempt at a Solution

I've had two quizes with problems just like this marked wrong in my college logic course. I confronted the professor about it and he just told me to study the truth tables. I'm very confused as to why this is wrong, because I've taken a discreet math course previously.
The conditionals for P and Q are both correct. Let's work with the third wff.

Assume that (P → Q) (Q → P).

Then, we have the same truth assignments as you just have! Indeed, like the other user just said, it's correct. Maybe, you should let your professor know about this! You are actually correct!

Thank you for checking it. I went to talk to him again about it and he told me that the T/F values for P and Q were not in 'order', it's suppose to be:

P | Q
------
T | T
T | F
F | F
F | T

He was actually quite angry and scribbled on my paper incoherently with T's and F's. I've never been warned of this ordering in his class, and I guess that's what he means by memorizing the truth tables. Which seems kind of counterproductive =/

Dick
Homework Helper
Thank you for checking it. I went to talk to him again about it and he told me that the T/F values for P and Q were not in 'order', it's suppose to be:

P | Q
------
T | T
T | F
F | F
F | T

He was actually quite angry and scribbled on my paper incoherently with T's and F's. I've never been warned of this ordering in his class, and I guess that's what he means by memorizing the truth tables. Which seems kind of counterproductive =/
That ordering is completely arbitrary. I agree with you. It is counterproductive. Watch out for that guy.