PP1 | $(p \wedge \neg p) \rightarrow q$ | from contradiction everything follows |
PP2 | $p \rightarrow (q \vee \neg q)$ | everything implies a logical tautology |
PP3 | $\neg p \rightarrow (p \rightarrow q)$ | from false propositions everything follows |
PP4 | $q \rightarrow (p \rightarrow q)$ | everything implies a true proposition |
PP5 | $(p \rightarrow q) \vee (q \rightarrow r)$ | imply or be implied! |
PP6 | $[ (p \rightarrow q) \wedge (r \rightarrow s) ] \rightarrow [ (p \rightarrow s) \vee (r \rightarrow q) ]$ | consequent exchange |
PP7 | $[ (p \wedge q) \rightarrow r ] \rightarrow [ (p \rightarrow r) \vee (q \rightarrow r) ]$ | Rutten's paradox |
As has been explained extensively at the
Mathematics Stack Exchange forum,
these Propositional Paradoxes shall be analyzed according to the sequential interpretation.
As usual, 1 stands for TRUE and 0 stands for FALSE. Don't cares are indicated by X. Here goes!
(if p then (if p then 0 else 1) else 0) then q else 1 : general (if 0 else 0) [ ] else 1 : p=0,q=X (if 1 then (if 1 then 0 ) [ ] else 1 : p=1,q=XIt is clear that $q$ is an unemployed variable. Hence, in the sequential interpretation of propositional logic, q is simply not present, as indicated by [].
if p then (if q then 1 else (if q then 0 else 1)) else 1 : general if 0 else 1 : p=0,q=X if 1 then (if 0 else (if 0 else 1)) : p=1,q=0 if 1 then (if 1 then 1 ) : p=1,q=1It is clear that all instances of the logical variables are functional in the sequential interpretation.
if (if p then 0 else 1) then (if p then q else 1) else 1 : general if (if 0 else 1) then (if 0 [ ] else 1) : p=0,q=X if (if 1 then 0 ) [ ] else 1 : p=1,q=XIt is clear that $q$ is an unemployed variable. Hence, in the sequential interpretation of propositional logic, q is simply not present.
if q then (if p then q else 1) else 1 : general if 0 else 1 : p=X,q=0 if 1 then (if 0 else 1) : p=0,q=1 if 1 then (if 1 then 1 ) : p=1,q=1It is clear that all instances of the logical variables are functional in the sequential interpretation.
if (if p then q else 1) then 1 else (if q then r else 1) : general if (if 0 else 1) then 1 [ ] : p=0,q=X,r=X if (if 1 then 0 ) else (if 0 [ ] else 1) : p=1,q=0,r=X if (if 1 then 1 ) then 1 [ ] : p=1,q=1,r=XIt is clear that $r$ is an unemployed variable. Hence, in the sequential interpretation of propositional logic, r is simply not present.
if [ first half ] then [ second half ] else 1If the [ first half ] is 0 (FALSE) then the program jumps to the 'else', giving 1 (TRUE). So, for the [ second half ], we only have to consider [ first half ] outcomes with (1).
if (if p then q else 1) then (if r then s else 1) else 0 : general if (if 0 else 1) then (if 0 else 1) : p=0,q=X,r=0,s=X (1) if (if 0 else 1) then (if 1 then 0 ) : p=0,q=X,r=1,s=0 (0) if (if 0 else 1) then (if 1 then 1 ) : p=0,q=X,r=1,s=1 (1) if (if 1 then 0 ) else 0 : p=1,q=0,r=X,s=X (0) if (if 1 then 1 ) then (if 0 else 1) : p=1,q=1,r=0,s=X (1) if (if 1 then 1 ) then (if 1 then 0 ) : p=1,q=1,r=1,s=0 (0) if (if 1 then 1 ) then (if 1 then 1 ) : p=1,q=1,r=1,s=1 (1)Second half:
if (if p then s else 1) then 1 else (if r then q else 1) : general if (if 0 else 1) then 1 [ ] : p=0,q=X,r=X,s=X if (if 1 then 0 ) else (if 0 [ ] else 1) : p=1,q=X,r=0,s=0 if (if 1 then 1 ) then 1 [ ] : p=1,q=X,r=0,s=1It is clear that the last instance of $q$ is unemployed. Hence, in the sequential interpretation of propositional logic, q is simply not present there [].
According to our hypothesis, PP1, PP3, PP5, PP6, PP7 are paradoxes in logica naturalis while PP2 and PP4 are not.