By popular request: my postscript hack to produce a four-fours advent calendar.
Each of 24 printed pages bears a label such as
4+4×4+4. Print, fold e.g. as shown below, insert pralines, tape to a convenient wall.
I'm not very happy about the postscript code for the square root sign and still less about the presence of 4² and 44, but the result is good enough to be fun. (Update: Everyone who got a calendar in 2011 suggested improvements, which I have incorporated.)