formula asserted with two different strengths at the same time.
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Since changing the truth value of an assertion from TRUE to FALSE or vice-versa is effectively reversing the assertion, that kind of change is not allowed through this facility.  Only the truth strength of the assertion can be changed here, not the complete truth value.  To change the truth value (not strength), go back to the Assertion Display Frame, click on "Edit", and change the truth value.  For help with the Edit Formula tool, see the