theorem
  for Y1,Y2 being non empty Subset of QC-symbols(A) st Y1 c= Y2 holds
    min Y2 <= min Y1
proof
  let Y1,Y2 be non empty Subset of QC-symbols(A) such that
A1: Y1 c= Y2;
  min Y1 in Y1 by Def35;
  hence min Y2 <= min Y1 by A1,Def35;
end;
