theorem
  MemberFunc (X /\ Y, A).x <= min (MemberFunc (X, A).x, MemberFunc (Y, A).x)
proof
  MemberFunc (X /\ Y, A).x <= MemberFunc (X, A).x & MemberFunc (X /\ Y, A)
  .x <= MemberFunc (Y, A).x by Th47,XBOOLE_1:17;
  hence thesis by XXREAL_0:20;
end;
