I'm a mathematician working in algebra. I've been using TeX since 1987, but couldn't write my Ph.D. thesis with it. Sob!
I teach LaTeX at my university, besides the mathematics courses. I'm the author of some LaTeX packages and even of one Plain TeX package. At my site it's possible to download my book on LaTeX programming (in Italian, sorry).
Here's my motto for TeX.SX:
Pronto prontissimo son come il fulmine: sono il factotum della città. (From "Il barbiere di Siviglia", music by Gioachino Rossini, libretto by Cesare Sterbini.)
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