Multiplication symbol in SMARTS

There is a SMARTS pattern that was published which looks like the following[1]



```
[#6 × 4]     

```

and there are actually spaces around the `×` symbols between the `6` and `4`. 


Question is, should I change this multiplication notation to a lower case "x", or really use some sort of ASCII symbol? I didn't see a multiplication symbol anywhere in the Daylight SMARTS description.


References:


1. Hou, T. J.; Xia, K.; Zhang, W.; Xu, X. J. [ADME Evaluation in Drug Discovery. 4. Prediction of Aqueous Solubility Based on Atom Contribution Approach](https://doi.org/10.1021/ci034184n). *J. Chem. Inf. Comput. Sci.* **2004**, *44* (1), 266–275. [PDF](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.591.6993&rep=rep1&type=pdf)




The question was answered on the [Open Babel mailing list](https://sourceforge.net/p/openbabel/mailman/openbabel-discuss/thread/BYAPR11MB336860D56A2CF32861354A50E8DD0%40BYAPR11MB3368.namprd11.prod.outlook.com/#msg36472667)


Suffice to say, there's no multiplication symbol in SMILES or SMARTS - only standard ASCII characters. It's likely a lower-case 'x' that's been mangled by a journal.


 3