The stuff "just before" is to link MathJax into the web pages that are to include mathematics. For the time being, that is going to be just this one page.
I put this in after I removed the problematic stuff below. So that problem has nothing to do with the above.

Sandbox

This is a page to experiment with html matters.

The following uses phpmathpublisher.
Here's a bloody test: S(f)(t)=a_{0}+sum{n=1}{+infty}{a_{n} cos(n omega t)+b_{n} sin(n omega t)}For whatever reason, the word test is inside the mmathfilter. What is going on?


I have a problem: I cannot comment out:
/** Blah blah */

Here is something else---which I don't understand: none of what follows shows. Even when commented out:

What was before that does not show.Not only that but it prevents everything after from showing.
Since uncomment does not work, I took out the problematic stuff and copied it in "Problematic HTML stuff"

I want to try MathJax
The default math delimiters are $$...$$ and \[...\] for displayed mathematics, and \(...\) for in-line mathematics. Note in particular that the $...$ in-line delimiters are not used by default. That is because dollar signs appear too often in non-mathematical settings, which could cause some text to be treated as mathematics unexpectedly. For example, with single-dollar delimiters, ”... the cost is $2.50 for the first one, and $2.00 for each additional one ...” would cause the phrase “2.50 for the first one, and” to be treated as mathematics since it falls between dollar signs.
So, here is my first attempt:
Here is a formula \(x\xrightarrow{\hspace{5mm}JILL\hspace{5mm}} JILL(x)= 2x+5\) that is part of a sentence
and here is the same formula displayed \[x \xrightarrow{\hspace{5mm}JILL\hspace{5mm}} JILL(x)= 2x+5\] in the middle of a paragraph. Truly amazing! OK, here we go:
The purpose of real valued functions is to represent the way situations change and that of the differential calculus, the "mathematics of change", is to derive \emph{local} information about (mostly gradual) changes from \emph{punctual} information. The nature of the desired information depends on the situation. If only because a real number has a \emph{sign} and a \emph{magnitude}, the desired information can be qualitative---is \(f\) near \(x_{0}\) positive/negative? increasing/decreasing, concave up/concave down?--- or quantitative---what is the approximative value, rate of change, acceleration of \(f\) near \(x_{0}\)? But, qualitatively, we might also want to know whether, at \(x_{0}\), \(f\) is continuous (resp. differentiable) while, quantitatively, we might ask what the jump (resp. the slope) is. We hope to show that to study a function by way of its local polynomial approximations is considerably more natural than, to quote Lagrange, "seeing derivatives in isolation". Specifically, we will argue that the systematic use of polynomial approximations has for the differential study of functions of one real variable much the same advantages that the use of decimal numbers has for the study of real numbers in that it organizes it, unifies and simplifies it «Gleason, 1967 \#34», and, moreover, extends canonically to the Frechet derivative in multi-variable calculus «Flanigan, 1971 \#78», Banach Spaces3 «Dieudonne, 1960 \#112», jets in Differential Topology «Bröcker, 1975 \#68».