A joke on metric spaces

微分方程式の教授が、いつも講義の半分が過ぎたところでジョークを言って
少し休む時間をくれる。
Parallel lines are sad, because they will never meet,
and even make the matter worse, they do not know that.

から始まり、
Some mathematicians pitied that and created a metric space in which parallel lines can meet each other.
Then, one night, the mathematician was dreaming, and found himself in an unusual world where parallel lines meet with each other infinitely many times. He was surprised and asked one of the lines what was happening. Then she replied " Well, it is a "norm" here.″


あとから、数学やってないとさすがに分かんねえよなとか思って変に嬉しいというねｗ
ジョークとか普段あんまり分からないから、尚更ｗ