"= >" This is the ejection symbol. Example: a deduces that b can be expressed as a = > B.

If necessary, you can use this symbol: "< = >".

A is a necessary and sufficient condition but not a necessary condition of B (that is, B is a necessary and sufficient condition but not a necessary condition of A), which can be expressed as: A = > B；;

A is a necessary and sufficient condition but not a sufficient condition of B (that is, B is a necessary and sufficient condition but not a necessary condition), which can be expressed as: B = > A；;

A is a necessary and sufficient condition for b, that is, a < = > b.

Note: In all symbols in the text, two horizontal lines (=) should be extended to intersect with the arrow ().