TITLE: What's "the most right" symbol to use for "defined to be equal to"?
QUESTION [10 upvotes]: What's the most used symbol for "defined to be equal to", at least in your experience (and I'm sure there are a lot of experienced people here)? Also, which one do you think is the "the most right" of them, in the sense of making the most amount of sense (no pun intended)? The ones I frequently see in literature, papers and articles on the Web are '$\equiv$', '$:=$' and '$=_{def}$'. The first one I come across a lot, though for me it's still "reserved" for modular arithmetic. The second one seems like it's come straight out of some programming language and the last one I frequently see in philosophy papers on logic and the like. What are your thoughts on this?

REPLY [3 votes]: One advantage of $:=$ is that it's assymetric, meaning you can distinguish the thing being defined and the definition.