[Logic] Formal fallacy for programmers

In SAT/SMT by Example i described IMPLY operation, often written as "=>": Ctrl-F "IMPLY constraint". Also, in Wikipedia.

"P => Q" is like:

Q = ?

if P==True:
    Q=True

Important: you don't know state of Q before. Q modified to True only if P is True.

Now let's read Wikipedia about formal fallacy:

Any argument that takes the following form is a non sequitur

#If A is true, then B is true.
#B is true.
#Therefore, A is true.

But we know that if A => B, opposite is (B => A) not true.

Another common non sequitur is this:

#If A is true, then B is true.
#A is false.
#Therefore, B is false.

The B 'global variable' could be set before.

Affirming a disjunct is a fallacy when in the following form:
#A or B is true.
#B is true.
#Therefore, A is not true.*

If P => Q, state of Q do not influence state of P.

Also, from Wikipedia about argument from fallacy:

If P, then Q.
P is a fallacious argument.
Therefore, Q is false.

P doesn't influence Q if P=False.

(the post first published at 20221023.)


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