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Orderless

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Orderless

is an attribute that can be assigned to a symbol f to indicate that the elements ei in expressions of the form f[$e_1$, $e_2$, ...] should automatically be sorted into canonical order. This property is accounted for in pattern matching.

The elements of an Orderless function are automatically sorted:

• • SetAttributes[f, Orderless]

• • f[c, a, b, a + b, 3, 1.0]

A symbol with the Orderless attribute represents a commutative mathematical operation.

• • f[a, b] == f[b, a]

Orderless affects pattern matching:

• • SetAttributes[f, Flat]

• • f[a, b, c] /. f[a, c] -> d