let E be set ; :: thesis: for A being Subset of (E ^omega ) holds A ? = A |^ 0 ,1
let A be Subset of (E ^omega ); :: thesis: A ? = A |^ 0 ,1
thus A ? = (A |^ 0 ) \/ (A |^ (0 + 1)) by Th75
.= A |^ 0 ,1 by Th28 ; :: thesis: verum