let E be set ; :: thesis: for A being Subset of (E ^omega) holds
( A ? = {(<%> E)} iff ( A = {} or A = {(<%> E)} ) )
let A be Subset of (E ^omega); :: thesis: ( A ? = {(<%> E)} iff ( A = {} or A = {(<%> E)} ) )
A ? = A |^ (0,1) by Th79;
hence ( A ? = {(<%> E)} iff ( A = {} or A = {(<%> E)} ) ) by Th31; :: thesis: verum