After perusing a GRE quantitative comparison question, I noticed the following statement: Given $0 < a < b < 1$, the product of $a$ and $b$ is less than $b$. For this practice question, the examinee is only required to determine which of two columns (i.e., 'Column A' or 'Column B') is larger in value. Under 'Column A' was the quantity $a*b$ and under 'Column B' was the value $1$. The author of the tutorial then used the quantity $b^{-}$ underneath 'Column A' to denote a value of $b$ that is less than $a*b$. This was expressed for edification purposes.
I have never seen a variable superscripted with a hyphen or minus sign (only). Does it mean exactly as the author intended (i.e., the 'negative superscripted' quantity is less than another quantity)?
Is this appropriate convention in mathematics circles? A google search was unfruitful.
The question is a bit in the weeds, but my curiosity got the best of me.