'Reset self to an initial state.  Used by __init__.'

def reset(self):

    self.t = self.x
    self.T = [self.x]
    self.D = [Poly(1, self.x)]
    self.level = (-1)
    self.exts = [None]
    self.extargs = [None]
    if self.dummy:
        self.ts = numbered_symbols('t', cls=Dummy)
    else:
        self.ts = numbered_symbols('t')
    self.backsubs = []
    self.Tfuncs = []
    self.newf = self.f
