# Enhanced marking - constraints

**URL:** https://forum.eternagame.org/t/enhanced-marking-constraints/3007
**Category:** Feature Suggestions
**Created:** [December 14, 2018, 1:28pm UTC](https://forum.eternagame.org/t/enhanced-marking-constraints/3007 "2018-12-14T13:28:00Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![Jterna](https://forum.eternagame.org/letter_avatar_proxy/v4/letter/j/48db29/32.png) [@Jterna](https://forum.eternagame.org/u/Jterna)
#### Post date: [December 14, 2018, 1:28pm UTC](https://forum.eternagame.org/t/enhanced-marking-constraints/3007/1 "2018-12-14T13:28:00Z")

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In addition to the simple black-circle base marking, allow to set constraints on a base.  
ie. Let me specify that a certain base can be only C/G/A or can’t be U/A, or instance.

If the constraints are violated during solving (by the player placing a non-satisfying base), the circle should be highlighted to indicate the violation.