let E be set ; :: thesis: for A, B being Subset of E holds (A \/ B) ` c= A `
let A, B be Subset of E; :: thesis: (A \/ B) ` c= A `
A c= A \/ B by XBOOLE_1:7;
hence (A \/ B) ` c= A ` by Th31; :: thesis: verum