Anything using = for a relation that is not symmetric is cursed IMO. More generally, any relation using a symbol that is visually vertically symmetric should be symmetric.

If you use big O notation at both sides, as in my example, it becomes symmetric.

In the same way that ceiling(1.2) = ceiling(1.9) is symmetric, even if their contents are not equal.

Yeah, like centered ° for function composition is a pet peeve of mine...

> O( f(n) ) = O(n^2) + O(n)

Naively, one would assume that that implies O( f(n) ) - O(n) = O(n^2), which is not correct. However, O( f(n) ) = O(n^2) + O(n) implies O( f(n) ) = O(n^2), which would have been obvious if proper notation had been used.