I recently was attempting to describe someone's smile. I wanted to describe it as being very 'infectious', or that it spreads very quickly and is contagious. However, as hard as I could try, I could only come up with words that have to do with infections or words that have a negative connotation. 

How could I describe a person's smile if it has the ability to 'spread' to other people, as denoted above?

Thanks!


Question: First package for typesetting commutative diagrams
Answer: You can find a comparison between packages for commutative diagrams in a very nice paper by Gabriel Vicente Feruglio on TUGboat, issued in 1994.

According to the bibliography, the first available package (besides using directly picture mode) was the one by John Reynolds, diagmac.sty issued in 1987 and still available as diagmac2 (some patches were introduced by Bob Tennent in order to make the package use pict2e facilities).

The porting of AMS-TeX to LaTeX pushed several people to do the switch and this prompted the development of the other packages described in Feruglio's paper.