T is elliptic if G(T) > 0 (equivalently K and _{1}K have the _{2}same sign);
T is hyperbolic if G(T) < 0 (equivalently K and _{1}K have _{2}opposite signs);
T is parabolic if G(T) = 0 (equivalently exactly one of K and _{1}K is _{2}zero);
T is planar if G(T) = 0 (equivalently K).
_{1}=K_{2}=K_{t}=0 |

an elliptic point |
a hyperbolic point |

a parabolic point |
a planar point |

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