Use $E[(X\leq Y)^2]$ to obtain lower and upper bounds of $E[XY]$ when $X$ and $Y$ are not statistically independent.

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Use $E[(X\leq Y)^2]$ to obtain lower and upper bounds of $E[XY]$ when $X$ and $Y$ are not statistically independent.

I don't understand what $(X\leq Y)^2$ supposed to mean. Is it a typo error?