
theorem
{f where f is FuzzySet of REAL : ex A be Subset of REAL st f=chi(A,REAL) }
c= Membership_Funcs (REAL)
proof
 let x be object;
 assume x in {f where f is FuzzySet of REAL :
 ex A be Subset of REAL st f=chi(A,REAL)};
 then consider f0 be FuzzySet of REAL such that
 A1: x=f0 and ex A be Subset of REAL st f0=chi(A,REAL);
 thus thesis by Def1,A1;
end;
