# Push-back lists on DCG rule heads

**URL:** <https://swi-prolog.discourse.group/t/push-back-lists-on-dcg-rule-heads/6532>\
**Category:** Nice to know\
**Created:** [May 7, 2023, 11:37am UTC](https://swi-prolog.discourse.group/t/push-back-lists-on-dcg-rule-heads/6532 "2023-05-07T11:37:10Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![EricGT](https://avatars.discourse-cdn.com/v4/letter/e/f1d935/32.png) [@EricGT](https://swi-prolog.discourse.group/u/EricGT)\
**Post date:** [May 7, 2023, 11:37am UTC](https://swi-prolog.discourse.group/t/push-back-lists-on-dcg-rule-heads/6532/1 "2023-05-07T11:37:10Z")

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Found this really old SWI-Prolog forum post (20 years ago) that had some useful information.

[https://swi-prolog.iai.uni-bonn.narkive.com/cOnL0aGn/push-back-lists-on-dcg-rule-heads](https://swi-prolog.iai.uni-bonn.narkive.com/cOnL0aGn/push-back-lists-on-dcg-rule-heads)

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**Author:** ![stassa.p](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/stassa.p/32/712_2.png) [@stassa.p](https://swi-prolog.discourse.group/u/stassa.p)\
**Post date:** [May 10, 2023, 6:43pm UTC](https://swi-prolog.discourse.group/t/push-back-lists-on-dcg-rule-heads/6532/2 "2023-05-10T18:43:00Z")

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Ah, those confusing push-back lists! Here’s another archived post from 12 years ago where the first poster is really, really confused and completely out of her depth:

[https://swi-prolog.iai.uni-bonn.narkive.com/QBwIiHBC/how-to-hide-implied-tokens-in-dcg-rules#post1](https://swi-prolog.iai.uni-bonn.narkive.com/QBwIiHBC/how-to-hide-implied-tokens-in-dcg-rules#post1)

(12 years ago! Bloody hell, time flies. Btw, where are Richard O’Keefe, Samer Abdallah and Feliks Kuzniak?)