⇔
Symbol  Format  Data 

⇔  Code Point 
U+21D4 
TeX 
\Leftrightarrow 

SVG 
The ifandonlyif symbol is used as a logical statement in math. Typically the symbol is used in an expression like:
In plain language, this means that if is true, then must be true and if is false, then must be false.
The if and only if symbol is used as a logical statement.
The left right arrow is used to indicate that two statements are logically equivalent, meaning that they are both true or both false.
Long left right arrow symbol.
Long left double arrow symbol.
The implies symbol is used in math to represent a logical implication. It signifies that if the first statement is true, then the second statement must also be true.