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Make the chemical formula example truly syntactically incorrect #28

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Make the chemical formula example truly syntactically incorrect #28

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8 changes: 4 additions & 4 deletions book/book.tex
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Expand Up @@ -1083,23 +1083,23 @@ \section{Formal and natural languages}
For example, in mathematics the statement
$3 + 3 = 6$ has correct syntax, but
$3 + = 3 \$ 6$ does not. In chemistry
$H_2O$ is a syntactically correct formula, but $_2Zz$ is not.
$H_2O$ is a syntactically correct formula, but $Zz^2$ is not.
\index{syntax}

Syntax rules come in two flavors, pertaining to {\bf tokens} and
structure. Tokens are the basic elements of the language, such as
words, numbers, and chemical elements. One of the problems with
$3 += 3 \$ 6$ is that \( \$ \) is not a legal token in mathematics
(at least as far as I know). Similarly, $_2Zz$ is not legal because
(at least as far as I know). Similarly, $Zz^2$ is not legal because
there is no element with the abbreviation $Zz$.
\index{token}
\index{structure}

The second type of syntax rule pertains to the way tokens are
combined. The equation $3 += 3$ is illegal because even though $+$
and $=$ are legal tokens, you can't have one right after the other.
Similarly, in a chemical formula the subscript comes after the element
name, not before.
Similarly, in a chemical formula the number of atoms is indicated
using a subscript, not a superscript.

This is @ well-structured Engli\$h
sentence with invalid t*kens in it. This sentence all valid tokens
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