Double Union

The Double Union at U+22D3 denotes a union-like mathematical operator with a doubled form, used where an author needs a distinct variant of set-theoretic joining. It sits in the Mathematical Operators block and is a printable symbol, not ordinary punctuation or a letter. Its main appearances are in advanced mathematics, especially order theory, lattice theory, algebra, and formal semantics, where specialized papers may assign it a local meaning analogous to union, join, or a combined supremum operation. For example, an author might use A ⋓ B for a particular disjoint, typed, or otherwise constrained union when the ordinary union sign is already reserved for another operation. Because its meaning is not standardized across all mathematics, the definition usually comes from the surrounding text, legend, or notation table. It is best read as “double union” unless a specific source defines it more narrowly; readers should not assume it has exactly the same value as ordinary set union or lattice join.