Need expert advice on doing it as simply as possible.

Good points Walt/Michael.  A way to solve these issues and still get it in one test, perhaps something like:

3. If T/F = True, then if code3= "tue" or "wed" or "thu", AND code3 ≠ code4 AND code3 ≠ code5, set T/F = TRUE, else set T/F = False

4. If T/F = True, then if code4= "tue" or "wed" or "thu", AND code4 ≠ code3 AND code4 ≠ code5, set T/F = TRUE, else set T/F = False

5. If T/F = True, then if code5= "tue" or "wed" or "thu", AND code5 ≠ code3 AND code5 ≠ code4, set T/F = TRUE, else set T/F = False

That should get the effect desired without more variables.  Blank won't work, and this ensures those last variables can only be used once.