examples don't show that entities are deprecated

The spec says
	"MathML characters can also be represented via entity
         references, although this practice is deprecated in MathML

		-- http://www.w3.org/TR/MathML2/chapter3.html

and yet it's full of examples that use them. Readers are going
to pay attention to the examples at *least* as much as they
will pay attention to that very quiet and subtle admonition.

If you really mean to deprecate π and such, don't use
it in so many examples.

Dan Connolly, W3C http://www.w3.org/People/Connolly/