# what is the symbol '-> and <->' stand for in substitution

When i try to do substitution, we need to type some basic symbols like the SQL symbols, there are 2 symbols which my colleagues ask me how to use. **->** and **<->** , anyone know how to use these 2 so that i can share the knowledge with my team members. thanks

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##### Gladys Xing replied

Hi Lei,

"→" is mathematically speaking an implication operator.

For example Statement A → Statement B

means (A/B could be a statement like (Posting DATE < current date)

- IF A is true and B is true then the result is true

- IF A is false and B is false then the result is true

- IF A is true and B is false then the result is false

- IF A is false and B is true then the result is true

↔ is mathematically an equivalence, meaning…

- IF A is true and B is true then the result is true

IF A is false and B is false then the result is true

- IF A is true and B is false then the result is false

- IF A is false and B is true then the result is false

Hope above information is helpful for you.

Best Regards,

Gladys