# The essence of the append infinite loop thread

**URL:** <https://swi-prolog.discourse.group/t/the-essence-of-the-append-infinite-loop-thread/7752>\
**Category:** General\
**Created:** [September 1, 2024, 6:02am UTC](https://swi-prolog.discourse.group/t/the-essence-of-the-append-infinite-loop-thread/7752 "2024-09-01T06:02:19Z")\
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**Author:** ![Boris](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/boris/32/7486_2.png) [@Boris](https://swi-prolog.discourse.group/u/Boris)\
**Post date:** [September 1, 2024, 6:32am UTC](https://swi-prolog.discourse.group/t/the-essence-of-the-append-infinite-loop-thread/7752/2 "2024-09-01T06:32:55Z")

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Yes, and this is why it is so easy to let it run away. As in this example of a class of mistakes I have done many times:

```
?- length(L, N), N =< 3.

```

written with the intent of “I want lists up to three elements long”.

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