You can make a standard envelope using a square piece of paper by following these steps from wikiHow :

Could you clarify if you meant (the mathematician), a specific RAR archive file , or something else entirely?

: You can use old book pages to make "teeny tiny" envelopes by following guides from creative crafters .

Depending on your project, you might prefer different styles:

: Position the paper like a diamond and fold it in half, corner to corner, then unfold it to leave a crease.

: Fold the bottom corner up so that it slightly overlaps the center where the side flaps meet. Top Flap : Fold the top corner down to close the envelope. Popular DIY Methods