'In HEP crystal-ball is also defined for m = 1 (see plot on wikipedia)
But the function doesn\'t have a finite integral in this corner case,
and isn\'t a PDF anymore (but can still be used on a finite range).
Here we restrict the function to m > 1.
In addition we restrict beta to be positive'

def _argcheck(self, beta, m):

    return ((m > 1) & (beta > 0))
