Crash course in mathematical notation for programmers

Love the idea of the post!

But there some issues:

Sum and product should use range(n+1). Math notation includes both endpoints; Python excludes the right endpoint.

The sum code could be written closer to the mathematical "idiom" as sum(a(i) for i in range(n)).

Using 'l' (lowercase L) as a variable is bad because it looks like '1' (literal one) in many fonts. Call your list 'u' or something, not 'l'.

The binary search code ends abruptly. Maybe it was eaten by the CMS?

And general suggestions:

Split big-O notation into different article, since it's a large topic.

The circle operator is often used for function composition; Python's Pythonicness makes it easy to say something like circ = lambda f, g : lambda a, k : f(g(a, k))

You should also mention that sometimes symbols depend on context. Operators in Python can have different semantics if they're overloaded; identical names can have different meaning due to scope effects, or if different libraries are imported. Likewise, notations in math can have different meanings; you have to be aware of both commonly accepted "default" meanings (just like '+' has built-in meanings for ints, floats, lists and strings) and any less-standard meaning that may have been defined in previous "code" (mathematical text).