let E be set ; :: thesis: for A being Subset of holds
( <%> E in A + iff <%> E in A )
let A be Subset of ; :: thesis: ( <%> E in A + iff <%> E in A )
A + = A |^.. 1 by Th50;
hence ( <%> E in A + iff <%> E in A ) by Th10; :: thesis: verum