Remove the extra spaces around ":" in PDF.
Remove the extra spaces around ":" in PDF.

":math:`Γ_P` is :math:`[p_1 :P_1 ;~…;~p_r :P_r ]`" is changed to
":math:`Γ_P` is :math:`[p_1{:}P_1 ; …; p_r {:}P_r ]`".

Since "p_1:P_1" is an element of the context separated by ";",
I think spaces around ":" should not bigger than spaces around ";".

But TeX inserts thick spaces around ":" in PDF.
It is bigger than spaces around ";" (without explicit "~").

TeX inserts spaces in math based on character classes.

The character class of "1", "P", etc. are Ord.
The character class of ":" is Rel.
The character class of ";" is Punct.

TeX inserts a thick space between Ord-Rel and Rel-Ord.
TeX inserts a medium space between Punct-Ord.
TeX inserts no space between Ord-Punct and Ord-Ord.

So, spaces around ":" are bigger than spaces around ";".

"{:}" removes spaces around ":" because it treats ":" as Ord.
This has same effect as "\mathord{:}".
So this makes spaces around ":" smaller or equal to the spaces around ";".

I removed "~" because I think that it inserts too big space and
there is no confusion without it.

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