Propel: negate multiple conditions

I need to negate multiple conditions at once u开发者_如何学编程sing Propel. E. g. a corresponding sql condition is:

WHERE !(something = 'a' and someOtherThing = 'b')

I couldn't find a way to solve this using Propel ORM. Is there a way to build this query with the Criteria-API that Propel 1.3 provides?

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here is the equivalent: something != 'a' or someOtherThing != 'b'