Implication and Iff
The Symbols are and
Implication says "if ... then"
If both a and b are odd numbers then (a+b) is even
can be written as:
both a and b are odd numbers (a+b) is even
The reason it points to the right is that it might not be true the other way
Just because (a+b) is even does not mean that a and b are odd (they may both be even)
Iff stands for "if and only if"
It is an implication that goes both ways.
x + y = 3 x = 3 − y
That one is true both ways!