I don't know if you know, but just in case you (or someone else) don't: There is no inequality symbol on the computer keyboard, so he used a typical programmer's inequality symbol which is "!=". So yes, it is not easily readable (i! is a bad combination...) but totally correct.
(i! is a bad combination...)
The way to handle that is whitespace: i != 0. (I once was teased by my tendency to put whitespace in computer code around all operators which would be spaced in typeset mathematical formulas.)
EDIT: I also use italics for variables, boldface for vectors, etc. when handwriting. Whenever I get a new pen I immediately check whether it's practical to do boldface with it.
Here's the new thread for posting quotes, with the usual rules: