#365

[ca_teran1]

I cant go back to problem to discuss it but I was totally lost

[ohthatpatrick]

This one said

"If W is after P, R will be after T"

We could symbolize that as

P -- W --> T -- R

Any time we have a conditional,
1 --> 2
we write the contrapositive, which is
-2 --> -1

So we need to write
- (T -- R) ---> - (P -- W)

However, with ordering rules like this, there's an easier way to think about saying
- (T -- R)

After all, that is saying "It is NOT the case that T is before R."
Okay, well then where IS it?
It must be that T is after R. Those are our only two choices.

Negating an ordering relationship basically gives you the opposite ordering relationship
- (T -- R) = R -- T

So instead of writing
- (T -- R) ---> - (P -- W)
we could write
R -- T ---> W -- P

==== looking at your mistake =====

The original was
P -- W --> T -- R

and you said we could infer
P -- W ---> R -- T

That's a contradiction!

The same left side idea forces us to do two opposite right side ideas?