What does this joke mean?

I saw this written on a blackboard in the math department building the other day:

Gas Law: $PV=nRT$

Ideal Gas Law: $(P)(V)=(n)(R)(T)$

I know the ideal gas law is something from chemistry, but I'm assuming this is meant to be some sort of joke involving math. Any ideas?

Solution 1:

In a ring, "$(a)$" is common notation for the principal ideal generated by $a$. (See https://en.wikipedia.org/wiki/Principal_ideal.)