let E be set ; :: thesis: for A, B being Subset of (E ^omega) st A c= B * holds
A + c= B *
let A, B be Subset of (E ^omega); :: thesis: ( A c= B * implies A + c= B * )
assume A c= B * ; :: thesis: A + c= B *
then A + c= (B *) + by Th58;
hence A + c= B * by Th60; :: thesis: verum