# \#functor

**URL:** https://swi-prolog.discourse.group/tag/functor/111.md

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## [Surprising result with equals dot dot](https://swi-prolog.discourse.group/t/surprising-result-with-equals-dot-dot/4989)

<div class="topic-metadata">

**Author:** [@brebs](https://swi-prolog.discourse.group/u/brebs)\
**Replies:** 16\
**Last updated:** [February 8, 2022, 9:39pm UTC](https://swi-prolog.discourse.group/t/surprising-result-with-equals-dot-dot/4989 "2022-02-08T21:39:03Z")

</div>

Using SWI-Prolog version 8.5.7 ?- X = (2, 3), X =.. Y, length(Y, YLen), nth1(1, Y, Y1). X = (2,3), Y = \[,,2,3\], YLen = 3, Y1 = (,). Is it correct for Y1 to ever be a tuple? Why default to such a confusing display of …