# BlankNullSequence

___ (three _ characters) or

is a pattern object that can stand for any sequence of zero or more Wolfram Language expressions.

___h or

can stand for any sequence of expressions, all of which have head h.

# Details

• Blank sequences work slightly differently depending on whether or not the head of the expression in which they appear is a symbol with the attribute Flat.
• Consider matching the pattern f[a1,a2,,___,c1,] against the expression f[a1,a2,,b1,,c1,]. If f is a symbol with attribute Flat, then the ___ will be taken to stand for the expression f[b1,]. If f is not a symbol with attribute Flat, then ___ will be taken to stand for the sequence of expressions b1, . With a named pattern, such as x___, x can be used only as an element in an expression. The sequence of expressions b1, is "spliced in" to replace x, thereby usually increasing the length of the expression.
• If ___ matches a sequence of length more than one, then the sequence will be represented by a Sequence object. In most uses of ___, however, the Sequence object will automatically be spliced into another expression, and will never appear explicitly.

# Examples

## Basic Examples(3)

A function that works with any number of arguments:

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A function that works with any number of integer arguments:

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A function that works with an integer followed by any number of arguments:

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