Approximation symbol: Is π ≈ 3.14.. equal to π ≒ 3.14..?

This could be a trivial question, but what is exactly the difference of between these two expressions? Am I correct to state the both interchangeably whenever I need to express the approximation of pi? I'm bit confused as here it states pi can be express by ≒ as it's not a rational number, but pi can also be expressed by a series (asymptotic), so it should be ≈ as well.

π ≈ 3.14..
π ≒ 3.14..

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The second symbol is written \fallingdotseq in LaTeX, but I haven't seen it before. –  Larry Wang Jul 29 '10 at 10:28
I see. We use ≒ quite occasionally in Japan. –  c4il Jul 31 '10 at 8:48

Any mathematical notation is ok as long as it is common knowledge in your community. For instance, I believe I fully understand the meaning of the $\approx$ symbol. However, I haven't ever seen the second symbol you provided.

To be on the sure side you should provide a definition of any relation symbol you don't consider to be common knowledge. This may happen as a short remark ("..., where $\approx$ denotes ...") or maybe as a table of the used symbols in the front matter of your work. As with any definition in mathematics, there is no right or wrong in the symbol/notion/etc. you use, only proper or unsound definitions.

Also: When in doubt, use the symbol that is used more commonly in the standard textbooks of your field. There is no benefit in being avant-garde at notation.

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