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OneIdentity

OneIdentity
is an attribute that can be assigned to a symbol f to indicate that f[x], f[f[x]], etc. are all equivalent to x for the purpose of pattern matching.
  • The fact that Times has attribute OneIdentity allows a pattern like n_.x_ to match x.
EXAMPLESCLOSE ALL
Basic Examples   (1)
The pattern matches, because Times has attribute OneIdentity:
Any function with attribute OneIdentity will match:
The pattern matches, because Times has attribute OneIdentity:
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Out[2]=
Any function with attribute OneIdentity will match:
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Properties & Relations   (2)
OneIdentity allows defaults to apply to expressions that do not involve Times at all:
For Flat functions, any sequence of arguments will match:
When f is both Flat and OneIdentity, a and f[a] are identical for pattern matching:
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