Flat

Flat

is an attribute that specifies that nested occurrences of a function should be automatically flattened.

See

A symbol with the Flat attribute represents an associative mathematical operation:

>> SetAttributes(f, Flat)
>> f(a, f(b, c))
f(a, b, c)

Flat is taken into account in pattern matching:

>> f(a, b, c) /. f(a, b) -> d
f(d, c)

>> SetAttributes({u, v}, Flat)
>> u(x_) := {x}
>> u()
u()

>> u(a)
{a}

Iteration limit of 1000 exceeded.

>> u(a, b)

Iteration limit of 1000 exceeded.

>> u(a, b, c)

>> v(x_) := x
>> v()
v()

>> v(a)
a

Iteration limit of 1000 exceeded.

>> v(a, b)
v(a, b)

Iteration limit of 1000 exceeded.

>> v(a, b, c)