OpenEuphoria

Re: 'Unknown' and three-valued logic (was: Example where Euphoria ...)

• Posted by Derek Parnell <ddparnell at bigpond.com> Nov 24, 2002
• 458 views

> Derek, maybe you, and of course anyone else interested, would like to
> have a look at the following lines, especially at the truth table? I'm
> not sure if it is correct -- and I also don't know what value to use for
> 'not unknown'.
>
> Best regards,
>    Juergen
>
> ------------------------------------------------------------------------
>
> Three-Valued Logic  (JuLu, 24. November 2002)
> =============================================
>
> Truth Table
> -----------
>
> Abbreviations:
> T = True
> F = False
> U = Unknown
>
>
> A | B | not A | A and B | A or B | A xor B
> --+---+-------+---------+--------+--------
> T | T |   F   |    T    |   T    |    F
> T | F |   F   |    F    |   T    |    T
> T | U |   F   |    U    |   T    |    U
> F | T |   T   |    F    |   T    |    T
> F | F |   T   |    F    |   F    |    F
> F | U |   T   |    F    |   U    |    U
> U | T |       |    U    |   T    |    U
> U | F |       |    F    |   U    |    U
> U | U |       |    U    |   U    |    F
>

Looks fine to me, except that 'not U' should be 'U', paradoxically. Because
if A is unknown then 'not A' means that we know what A is, however we don't.

Non boolean operations will always produce an unknown value though when at
least one of the operands is unknown.

 A | B | A + B | A  -  B | A *  B | A = B
 --+---+-------+---------+--------+--------
 1 | 1 |   2   |    0    |   1    |    1
 1 | U |   U   |    U    |   U    |    U
 U | 1 |   U   |    U    |   U    |    U
 U | U |   U   |    U    |   U    |    U



----------------
cheers,
Derek Parnell