
theorem
{chi([.a,b.],REAL) where a,b is Real : a <= b}
c= Membership_Funcs (REAL)
proof
 let x be object;
 assume x in {chi([.a,b.],REAL) where a,b is Real : a <= b};
 then ex a,b be Real st x=chi([.a,b.],REAL) & a <= b;
 hence thesis by Def1;
end;
