Equivalence classes

A request for clarification about equivalence classes.

If all elements are declared via top-level `element' declarations,
then I think that I understand how equivalence classes work.  Can
someone please explain how equivalence classes work in the presence
of element declarations nested within type declarations?

Also, I gather that equivalence classes are not really symmetric.
That is, declaring A with equivalence class B is not at all the
same as declaring B with equivalence class A.  I think this is the
right choice, but the schema specification needs to be clarified
and it would help to choose a name that did not imply symmetry.
In particular, I suggest exploiting the analogy with object-oriented
languages, and replacing `equivClass' with `super'.

-- P

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Philip Wadler                             wadler@research.bell-labs.com
Bell Labs, Lucent Technologies      http://www.cs.bell-labs.com/~wadler
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