[stormer]

Not uncommon = common.

[The_Reader_David]

You do realize that natural language is not actually bound by Aristotelian logic, don't you?

My favorite proof of this is the undoubted fact that saying a woman is "not unattractive" is not equivalent to saying she is attractive.

In many contexts in the natural use of English, just as in intuitionistic logic, NOT(NOT P) is weaker than P.