⊕ (thing)

It looks like a Quake-fonted O, but it's not. It's direct sum notation. Given two sets of integers A and B, A ⊕ B consists of the set {a + b: a ∈ B; b ∈ B}. Example:

A = { 4, 5, 7 }
B = { 1, 2 }

A ⊕ B = { 5, 6, 6, 7, 8, 9 }