I am new to python. I have a few questions coming from an armature!

[Marko Rauhamaa]

Grant Edwards <grant.b.edwards at gmail.com>:

> On 2016-08-17, Marko Rauhamaa <marko at pacujo.net> wrote:
>
>> Somewhat analogously, I remember how confusing it was to learn formal
>> logic in college. I was having a hard time getting the point of
>> definitions like:
>>
>>    (x ∧ y) is true iff x is true and y is true
>>
>> That's because I had learned in highschool that "x ∧ y" was just an
>> abbreviation of "x and y".
>
> It is. The expression "x ∧ y" is the same as "x and y". And that
> expression is true "iff x is true and y is true". It's just a sligtly
> more explicit way of writing the expression...

Well, not quite.

Notice the word "and" after "iff". That word is on a different plane
than "∧". The word "and" is on the semantic plane while "∧" is part of
the syntax. (Of course, that would be true even if "∧" were written
"and".)

The formal sentence template

   (x ∧ y)

contains the symbols "(", "∧" and ")". However, "x" and "y" are not part
of the formalism; rather, they are semantic placeholders for arbritrary
formal sentences.

The rest of the definition:

   is true iff x is true and y is true

is plain-English semantics.

In particular, the definition is *not* identical with the formal
sentence:

   (x ∧ y) ↔ (x ∧ y)


Marko