OneIdentity

OneIdentity
is an attribute that can be assigned to a symbol f to indicate that

, etc. are all equivalent to x for the purpose of pattern matching.

The pattern matches, because Times has attribute OneIdentity:

Any function with attribute OneIdentity will match:

The pattern matches, because Times has attribute OneIdentity:

Out[1]=

Out[2]=

Any function with attribute OneIdentity will match:

Out[4]=

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

are identical for pattern matching: