# How does one pronounce $a \odot b$?

I have seen authors use $\star$, $\ast$, $\cdot$ and $\odot$ to represent arbitrary binary operations on sets. I'm wondering, what is the standard way to read or pronounce something like $a \star b$? How would you read $a \odot b$?

• How about "a odot b"? :P – Bruno Stonek Mar 30 '11 at 1:08
• I guess what I'm trying to ask is, is there a standard way to say $a \Box b$, where $\Box$ is meant to represent some arbitrary operation? Saying "a operation b" doesn't really flow. – Zach Langley Mar 30 '11 at 1:14
• For an unspecified (or strange) operator, I would say "times" or "composed with". – Jack Schmidt Mar 30 '11 at 1:17
• @Jack: "composed with" seems inappropriate if the operator isn't associative. – Qiaochu Yuan Jul 29 '12 at 7:32
• @lenticcatachresis for what it's worth, I do read it like that always :D. – Functional Analysis Nov 2 '15 at 13:46

Usually, when I write such an operator into a problem, I use some variant of an asterisk or star (often a circled asterisk), reading it as "star" in my head. If I'm not using some sort of star, I usually use a circled or boxed X-type symbol and read it as "cross" in my head.

I suggest "sun" for $\odot$ (the standard astronomical symbol).

I try to read from the context what it's supposed to mean. Most of the time I can extract how it's pronounced by just looking at the preceding text.

Without context I read $\odot$ as tropical multiplication and $\star$ as convolution (of some kind), but of course they can represent some other binary operation just as well. For $\cdot$ I could use either dot or times and $*$ could be times or star, I guess.

But most of the time there is a context, isn't it? If not, then my main priority would be to try and find the context.

• What if the context is only that is it an operation? For example, "Given a binary operation $\diamond$ that is associative and commutative, show that..." – Zach Langley Mar 30 '11 at 14:29
• Then I would pronounce it as it looks, i.e. star, dot, square and perhaps "circled dot" for $\odot$ – Elin G Mar 30 '11 at 16:32
• Yeah, I would say the operation itself. "ƒ∗g" uses the "asterisk operator", for instance, but in the context of engineering, I would not say "f asterisk g" or "f star g". I would say "f convoluted with g" or "the convolution of f and g". In other contexts, the same symbol would be read differently. – endolith May 17 '11 at 15:42

I would say a⊙b as "a op b"

if is is the only binery operation being defined on the set a and b are from, then I might drop it and write $ab$ and say "a b"

"op" since it is a operator, and odds of there being two operators being used that I don't have words like: star, asterix, cross, mod plus, circ etc, are pretty low.

But if it happened I would be saying "c alt-op d" or perhaps "c op-two d" (though if said fast that is hard to tell from "c op 2d"