What does a box with a plus inside signify?

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In a paper I recently came across a simple mathematical symbol I've never seen before. It's a square with a cross inside and looks like this: Symbol

The question asks which of the following options would hold true with respect to this equation: Three Possible Answers

I would appreciate it if someone knew the name of this symbol and what it's characteristics are.

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(a) holds true, just compare both sides by writing $$a\ln(b)-b\ln(a)$$ and $$-(b\ln(a)-a\ln(b)$$The result is clearly the same.

With the other two, unless I'm missing something, are false.

$$1\ln(b)-b\ln(1)=\ln(b)-0=\ln(b)\not=b$$ and $$a\ln(b^2)-b^2\ln(a^2)=2a\ln(b)-b^2\ln(a)$$ $$2[a\ln(b)-b\ln(a)]=2a\ln(b)-2b\ln(a)$$