Here's the question you clicked on:
2bornot2b
\[a\implies b\] does it mean \[b\implies a\] ?
But \[¬B \implies ¬A\] is not neccessarily true.
To illustrate the previous sentence: I'm a male => I'm human is true I'm human => I'm a male is false I'm not human => I'm not a male is true
a<=>b does it mean b<=>a?
a⟹b is not logically equivalent to b⟹a however a⇔b is logically equivalent to b⇔a
I often find useful to think with diagrams: |dw:1325435683348:dw| if a then b (if I'm in A, then I'm in B). So it's clear the opposite is not necessary true. But if I'm not in B, then I'm not in A