I have a question.
I've never seen the logical sign "almost equivalent to". Does it exist? If not, why not? To say it's useless, for me it's like saying the sign " " is useless since you always can write what you want using the " " sign. (Of course if I'm right).
I give you an example of when I find it useful : Say we write ≈ . Why wouldn't we write ≈ is "almost equivalent" to say ≈ ?