Wikipedia shows this graph for the arccotangent function, which I can also find in a few other web pages like this one. On the other hand I have these from Wolfram and Mathlab. Why do some references add PI on the negative side while others do not? I see definitions for negative values such as arccot(-x) = pi - arccot(x) in the first case and arccot(x) = arctan(1/x) for the second case. Which one is (more) correct?