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:


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. J. Chem. Inf. Comput. Sci. 2004, 44 (1), 266–275. PDF
The question was answered on the Open Babel mailing list

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.