Pronunciation of $M(x)$ and $m(x)$ Suppose I use two functions and I denoted them by lowercase and uppercase letters $m(x)$ and $M(x)$.  Of course, I have to distinguish them somehow.
How do I read this? Is capital/uppercase $M$ of $x$ and lowercase $m$ of $x$ ok?

I'd say "big em of ex" and "little em of ex". (I am spelling out "em" and "ex" so that I don't have to decide whether to write them uppercase or lowercase.)
In a situation where most other letters occurring were small, I might say "big em of ex" for $M(x)$ and "em of ex" for $m(x)$, but only if I were feeling particularly lazy; this inevitably seems to lead to confusion.
