I found, so many times, the following expression.
we will divide a dataset \(X\) into the 2 parts of positive effect and negative effect, as following,
Write the above, like this,
Let dataset be \(X\). We will divide \(X\) into the 2 parts of positive effect \(X^{+}\) and negative effect \(X^{-}\), that is,
Do not use multi-italic string for label. And if they are so famous meaning like positive and negative, use the common notation \(+, -\) for them. \(\cup\) does not assure the intersection is empty. Divide means the intersection is empty, so make the meaning of "divide" clear by using sum notation \(+\) for set union operation.