[mxmlnkn]

As far as I remember, that's not a problem in math:

:= definition ≡ identity = equality ∝ proportionality

[nyc111]

But this is how it works:

= definition = identity = equality = proportionality

[Twisol]

Big-O notation is a famous example where = is some flavor of (asymptotic) proportionality, and it catches a lot of people out when they first learn about it.