--- infinite?

    ͤ + ΤȤ 1-ΤȤ -1 ֤ޤʳ nil 
    ޤư 0 ˤ  Ǥ

          inf = 1.0/0
          p inf
          p inf.infinite?

          => Infinity
             1

          inf = -1.0/0
          p inf
          p inf.infinite?

          => -Infinity
             -1

