My sheets didn't give me an information about it and I can't copy the symbol into thread.
The symbol between P and Q. Could you tell me,what does it mean?

 

I can't understand the context of use, so I could well be wrong, but I've generally seen it to mean that Q is provable from the sequences of P's.

 

https://en.wikipedia.org/wiki/List_of_mathematical_symbols

It is about 25% of the way down the page.

 

Hi,

It appears we have a lot of symbols these days. It's too bad they dont want to use regular language sometimes
We end up with a bunch of symbols that are not as commonly used. Check out my sig line