def _p_minmax_ ( p ) :
    """Get min/max values for derived bernstein polynomials
    
    >>> p = ...
    >>> mn,mx = p.minmax()

    The values are such that: mn <= p(x) <= mx  for all x_min<=x<x_max
    """
    b    = p .bernstein() 
    pars = b .pars()
    mn   = min ( pars )
    mx   = max ( pars )
    return  max ( mn , 0 ) , mx