/sci/ - Science & Math

>>11511254
(A => B) => ((not B) => (not A))
is constructively true. In fact it's a special case of
(A => B) => ((B => C) => (A => C))

The Brouwer–Heyting–Kolmogorov style functional proof p of this is very easy:
p(f):=g(ag(f(a)))
where f:A->B, g:B->C, a:A.

In words
>given a reason f to believe that A implies B, then given a reason g that B implies C, then the following is the case: given a reason that A holds, you can conclude that B holds (via f) and, in turn, that C holds (via g).

Replace =>C with =>False to get the claim about negation.

The other direction can't constructively be true. No matter how many reasons to believe about some negations and implications between negations being true, you can't ever find a reason to believe =>B (unless you take double negation as an axiom)

>>11511254
(A => B) => ((not B) => (not A))
is constructively true. In fact it's a special case of
(A => B) => ((B => C) => (A => C)

The Brouwer–Heyting–Kolmogorov style functional proof p of this is very easy:
[math] p(f) := g \mapsto ( a \mapsto g(f(a)) ) [/math]
where f:A->B, g:B->C, a:A.

In words
>given a reason f to believe that A implies, B, then given a reason g that B implies C, then the following is the case: given a reason that A holds, you can conclude that B holds (via f) and, in turn, that C holds (via g).

Replace =>C with =>False to get the claim about negation.

The other direction can't constructively be true. No matter how many reasons to believe about some negations and implications between negations being true, you can't ever find a reason to believe =>B (unless you take double negation as an axiom)

>>11217243
Because any physical metric goes to shit in humans past 23. Downwards slope.
People want fertile healthy partners.
And in women, physical outweighs material means to provide and social status.

Consider the age of models.
Consider the age of porn a actors.

Pregnancies are much more risky from 31yo on.

>>11218227
>I can't go below 20 without feeling like a creep as a 25yo
In the same sense in which you can't go out nakined in the summer - a social convention you've been raised into. It's arbitrary and you can decide whether it's relevant to you. Protip: The only reason not to fuck 18yo's with 36 is because fathers and older women don't like it. Get unspooked.