WOLFRAM LANGUAGE TUTORIAL

Patterns Involving Alternatives

patt1|patt2|a pattern that can have one of several forms

Specifying patterns that involve alternatives.

This defines to give when its argument is either or .
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The first two cases give .
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You can also use alternatives in transformation rules.
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Here is another example, in which one of the alternatives is itself a pattern.
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When you use alternatives in patterns, you should make sure that the same set of names appear in each alternative. When a pattern like matches an expression, there will always be a definite expression that corresponds to the object . If you try to match a pattern like , then there still will be definite expressions corresponding to and , but the unmatched one will be Sequence[ ].

Here is used to name the head, which can be either or .
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