
theorem
{chi(A,REAL) where A is Subset of REAL : A c= REAL}
c= Membership_Funcs (REAL)
proof
 let x be object;
 assume x in {chi(A,REAL) where A is Subset of REAL : A c= REAL};
 then ex A be Subset of REAL st x=chi(A,REAL) & A c= REAL;
 hence thesis by Def1;
end;
