\subseteqqThe symbol \subseteqq is used in mathematical notation to denote a subset relation where one set is a subset of another, and it allows for the possibility of the two sets being equal. It is a more inclusive version of the subset symbol \subseteq, emphasizing that the first set is contained within the second set, possibly being identical to it.
Set A is a subset of or equal to set B.
A \subseteqq BThe set containing elements 1 and 2 is a subset of the set containing elements 1, 2, and 3.
\{1, 2\} \subseteqq \{1, 2, 3\}The empty set is a subset of any set A.
\emptyset \subseteqq A