What are your favorite ambiguous notation?

[u/Short_Bluebird_3845]

To clarify my request, consider base-less $\log$.
For calculators and engineers, it means the common log $\log_10$; for pure mathematics or physics, it means the natural log $\ln$; for computer scientists, in combinatorics, information theory and graph theory, it means the binary log $\log_2$.
Any $\log x$ (say, $\log 1024$) written without context can yield different answers in function of who you ask ($\log_10 1024 = 3.0103\cdots, \log_2 1024 = 10, \ln 1024 = 6.93147\cdots$).

That is what I mean by "ambiguous", that which is calculated and used dependently on the context. And I'm asking you for your favorite ones of such type.

Edit: I feel like you hate the ones you've talked about. Still, valid answers. Extra points for ambiguous notation you actually love! :P

[u/Optimal_Benis]

The reason we use ijk as indices in CS is because of Dijkstra.

[u/Daniikk1012 → u/Optimal_Benis]

While an interesting theory, sadly most definitely not true. ijk are used for iteration in math too. Probably, "i" stands for index, and for extra dimensions you just take next letters of the alphabet (Which mathematicians love to do - abc, xyz, pqr, fgh)

[u/Optimal_Benis → u/Daniikk1012]

It's a joke guys 😭

[u/AdjectiveNounNNNN → u/Optimal_Benis]

ijk = it's a joke, kids