Implication and Iff

The Symbols are implies symbol and iff symbol

Implication: implies symbol

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 implies symbol (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: iff symbol

Iff stands for "if and only if"

It is an implication that goes both ways.


x + y = 3 iff symbol x = 3 − y

That one is true both ways!