I was wondering what the meaning of the notation $\ ( )^+ \ $is? For instance, what would be the value for $\ (x)^+ \ $for different values of x, say: $\ x=-1, x=0, x=1 \ $? Thank you in advance.
The original expression I encountered is a little complex, however I could reduce it down to something as such:
$$ \bigcup_{i \in I} \{(a+b-\sum\limits_{i=1}^k D^i)^+\} $$
Here, the above expression represents a set and we know that any value for $D^i$ is nonnegative.