def _make_mutant_node(nd):
    """Create a new logic for mutation that can be activated from .cfg file."""
    curent_rt_up = nd.rt_up
    curent_rt_down = nd.rt_down
    lowvar = '$Low_' + nd.name
    highvar = '$High_' + nd.name
    rt_up = (lowvar + ' ? 0 : (' + highvar + ' ? 1E308/$nb_mutable : (' +
        curent_rt_up + '))')
    rt_down = (highvar + ' ? 0 : (' + lowvar + ' ? 1E308/$nb_mutable : (' +
        curent_rt_down + '))')
    newNode = nd.copy()
    newNode.rt_up = rt_up
    newNode.rt_down = rt_down
    newNode.is_mutant = True
    return newNode
