[TUHS] How should I define 'thing' before I start talking about it?

[Douglas McIlroy]

> As far as I see it, EQN input is made of things where a thing is one of

>        mathematical or troff or eqn symbol
>        mathematical punctuation
>        delimiter, these being space, '~', '^', '{', '}', or newline
>        a character surrounded by punctuation or delimiters
>        - with/without users errors
>        a word surrounded by punctuation or delimiters
>        - with/without users errors
>        EQN keywords (which are special words???)

> That is way too long winded!! I want something tight.

Quotes take precedence over all other things.

What is a "troff symbol"? I can only think of troff escapes, which can
only appear in quotes , so are not eqn things in their own right. (In
user errors they may be seen as punctuation, etc.)

Ditto for "eqn symbol"? Perhaps the union of some or all of the things
that follow in the list?

Ditto again for "mathematical punctuation". Comma is one example I can
think of.  Apostrophe, read as "prime", may be another. Are there
more?

Is "surrounded by" inclusive or exclusive? Why is "character"
distinguished from "word"?

The ??? question bears on the issue of whether sintheta is one thing
or two. The word "maximal" will probably figure in the answer

Another (sticky) point is how punctuation sticks to an adjacent thing.
For example, eqn inserts space in (a,b), but keeps the whole thing(?)
together in 2 sup (a,b).


Doug