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
.
The first two cases give
.
| Out[2]= |  |
You can also use alternatives in transformation rules.
| Out[3]= |  |
Here is another example, in which one of the alternatives is itself a pattern.
| Out[4]= |  |
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
.
| Out[5]= |  |
