Mathematical Maturity

"fearlessness in the face of symbols: the ability to read and understand notation" -> the ability jump into a new code base and figure out what it does

"introduce clear and useful notation when appropriate (and not otherwise!)" -> the ability to create new abstractions when required, but to use well-known abstractions when possible (and to not obfuscate code with unnecessary abstractions)

"a general facility of expression in the terse—but crisp and exact—language that mathematicians use to communicate ideas" -> the ability to express ideas concisely and elegantly in a programming language

Etc...