Naming the substitution

AsTeR chooses identifier names that convey some information about the object being replaced. This has two advantages:

• An identifier like ``summand'' when referring to the expression appearing as the summand in a summation conveys more information than the identifier [tex2html_wrap5866].
• When substitutions are spoken after rendering the top-level expression, the listener finds it easier to relate them to the top-level expression.

• Type information. The objects returned by the recognizer are all typed. So at the very least, we have type information for all objects, e.g., mathematical function, parenthesized expression, etc.
• Contextual information. The first child of a fraction is called its ``numerator''. The left-hand side of an implication is called the ``premise'' and its right-hand side the ``conclusion''. We have built in this information for standard mathematical objects and provided a flexible mechanism for the user to add or modify such information.
• Special patterns: The special patterns presented in s:special_patterns are also used in synthesizing meaningful names for the substitutions.

Thus, when substituting for the subscript to a summation operator, AsTeR uses the name ``lower constraint''. Since more than one such ``lower constraint'' may be substituted in a general expression, such names are appended with an integer to make them unique. This is how the rendering shown earlier for Faa De Bruno's formula is produced.