'Refine an isolating interval to the given precision.
``eps`` should be a rational number.'

def refine_root(f, s, t, eps=None, steps=None, fast=False):

    if (not f.lev):
        return dup_refine_real_root(f.rep, s, t, f.dom, eps=eps, steps=steps, fast=fast)
    else:
        raise PolynomialError("can't    refine    a    root    of    a    multivariate    polynomial")
