Gift guide

I didn't post any jokes for sometime so here goes:
Especially for those who are not mathematicians but have friends who are obsessed with math - A detailed guide for buying presents:

First of all what not to buy:
1. Epsilons. While they are more than zero and are very useful, they are not good presents. First of all they are so small that that they are very easy to lose - moreover it is even difficult to see them. Besides, true mathematicians use their own personally made epsilons.

2. Empty set. It is important, but there is nothing in it. Don't be greedy.

3. Calculators. It may sound surprising to you but we have no use for them. For simple calculations we have our mind, and for difficult a powerful computer is needed. Besides, calculators are almost useless when writing proofs.

Now, lets look on some good ideas for a gift:
1. Mersenne prime poster. The Mersenne project attempts to find primes of the form . The currently largest known prime is a Mersenne prime. It is about 9.8 million digits long.
You can find the poster here.

2. A cake with a mathematical theme. See the image below for example:

original unknown

3. Something not connected to math!!!! For those mathematicians who feel that they have done too much math lately.

4. Moneyis a great present - perhaps not as personal as you would like, but still a good present. Especially if the person you want to give the present to is still a student. He will appreciate such a gift a lot...