BlankNullSequence
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BlankNullSequence
is a pattern object that can stand for any sequence of zero or more Wolfram Language expressions.
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)Summary of the most common use cases
A function that works with any number of arguments:

https://wolfram.com/xid/0mlgi82q70uq-b8tg0g

https://wolfram.com/xid/0mlgi82q70uq-p4dxwc

A function that works with any number of integer arguments:

https://wolfram.com/xid/0mlgi82q70uq-cjdoai

https://wolfram.com/xid/0mlgi82q70uq-fnskvr

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

https://wolfram.com/xid/0mlgi82q70uq-ctk9ry

https://wolfram.com/xid/0mlgi82q70uq-p89cqs

Wolfram Research (1988), BlankNullSequence, Wolfram Language function, https://reference.wolfram.com/language/ref/BlankNullSequence.html.
Text
Wolfram Research (1988), BlankNullSequence, Wolfram Language function, https://reference.wolfram.com/language/ref/BlankNullSequence.html.
Wolfram Research (1988), BlankNullSequence, Wolfram Language function, https://reference.wolfram.com/language/ref/BlankNullSequence.html.
CMS
Wolfram Language. 1988. "BlankNullSequence." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/BlankNullSequence.html.
Wolfram Language. 1988. "BlankNullSequence." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/BlankNullSequence.html.
APA
Wolfram Language. (1988). BlankNullSequence. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/BlankNullSequence.html
Wolfram Language. (1988). BlankNullSequence. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/BlankNullSequence.html
BibTeX
@misc{reference.wolfram_2025_blanksequence, author="Wolfram Research", title="{BlankNullSequence}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/BlankNullSequence.html}", note=[Accessed: 14-May-2025
]}
BibLaTeX
@online{reference.wolfram_2025_blanksequence, organization={Wolfram Research}, title={BlankNullSequence}, year={1988}, url={https://reference.wolfram.com/language/ref/BlankNullSequence.html}, note=[Accessed: 14-May-2025
]}