| NaN, Inf, isNaN, isInf \- not-a-number and infinity functions |

| The IEEE floating point standard defines values called |

| `not-a-number' and positive and negative `infinity'. |

| These values can be produced by such things as overflow |

| Also, the library functions sometimes return them when |

| the arguments are not in the domain, or the result is |

| returns a double that is not-a-number. |

| returns true if its argument is not-a-number. |

| returns positive infinity if |

| is greater than or equal to zero, |

| returns true if its first argument is infinity |

| with the same sign as the second argument. |