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From my studying I think it says that in order to have a necessary stmt you must have a sufficient stmt, but if you have a sufficient stmt then there may not be a necessary stmt. Is that correct? Can someone please explain that?

Also, I had another ? regarding conditional stmts. This is just one I made up:

If you eat junk, then you will get fat and get stretch marks.

so the contrapositive would be if you do not get fat or you don't get stretch marks then you do not eat junk.

But what if you get fat and dont get stretch marks? The or is confusing me, I don't know if that makes sense. But any help/examples would be really appreciated.

If you eat junk, then you will get fat and get stretch marks.

so the contrapositive would be if you do not get fat or you don't get stretch marks then you do not eat junk.

But what if you get fat and dont get stretch marks? The or is confusing me, I don't know if that makes sense. But any help/examples would be really appreciated.

This is what I made for your first statement:
J --> F + S

Contrapos is:
-F or -S --> -J

We know nothing if you just state you are fat. Remember direction of arrows is important.
F--> ?
but we do know that if you don't have stretch marks then you cannot eat junk.
-S --> -J
At this stage it doesn't matter if you are fat or not, -S leads to -J.

Anyone for Hardy's/Carls Jnr?