How many constraints are there in $g(x) \leq 2x \geq 0$?
I thought $g(x) \leq 2x$ and $g(x) \geq 0$, but something suggested that there could be three rather than two constraints here?
Perhaps the third one is about constraining $2x$ from above?
The reason for there being third one is that this is in a "black box optimization" example. And the author evaluates three distinct inequality constraints. Rather than two.
Third one could be $2x - g(x) \geq 0$, but I'm not sure if this makes any difference? Shouldn't this be captured by the two constraints already? Unless one must make sure that $2x \geq 0$?