(IUPAC) How do you number an alkane that has two equally small starting points?

[![enter image description here](https://i.stack.imgur.com/YseOm.png)](https://i.stack.imgur.com/YseOm.png)


For example, do you number this from left to right or right to left? How do you know?


Would you get 2,4-dibromo-6,6-dichloro-5-methylheptane or 4,6-dibromo-2,2-dichloro-3-methylheptane?




The current version of *[Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book)](http://dx.doi.org/10.1039/9781849733069-fp001)* reads as follows:



> 
> **P-14.4** NUMBERING
> 
> 
> When several structural features appear in cyclic and acyclic compounds, low locants are assigned to them in the following decreasing order of seniority:
> 
> 
> (…)
> 
> 
> (f) detachable alphabetized prefixes, all considered together in a series of increasing numerical order;
> 
> 
> (…)
> 
> 
> 


Furthermore,



> 
> **P-14.3.5** Lowest set of locants
> 
> 
> The lowest set of locants is defined as the set that, when compared term by term with other locant sets, each cited in order of increasing value, has the lowest term at the first point of difference; (…)
> 
> 
> 


Therefore, the example is named as **4,6-dibromo-2,2-dichloro-3-methylheptane** rather than 2,4-dibromo-6,6-dichloro-5-methylheptane since the locant set ‘2,2,3,4,6’ is lower than ‘2,4,5,6,6’.


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