A fountain penA fountain pen, of course. If you do mathematics you have to write a lot. I write about 6,000 pages per year (I know it is crazy that I know that number) and the the best writing tool ever created is a fountain pen. My father gave me my first fountain pen when I was 12 and now I have more than 30 of them. I poisoned my kids with the love to fountain pens too, but they are jealous, because they think I might love fountain pens more then them, and I will not comment on that. Merry Christmas!
