def METHOD_NAME(self, parent: tp.ArrayLike, arity: int = 2) -> tp.ArrayLike:
    """Good old one-variable mutation.
    Parameters
    ----------
    parent: array-like
        the point to mutate
    arity: int
        the number of possible distinct values
    """
    dimension = len(parent)
    if dimension == 1:  # corner case.
        return self.random_state.normal(0.0, 1.0, size=1)  # type: ignore
    out = np.array(parent, copy=True)
    ind = self.random_state.randint(dimension)
    out[ind] = self.significantly_mutate(out[ind], arity)
    return out