In the equation editor, half sided intervals such as
require both upper and lower bounds to be entered. Why? I would have thought that a boundary value would only need to be entered for the bounded side.

For example I have a function f(x)=y, but want the maximum value to be 0. I expect to use the left sided half open interval:
f(x) = y E(,0]

Should I put a dummy vale in the left hand side of the interval?
f(x) = y E(-10000,0]