{ 1. Ham kiem tra mang doi xung  }

Function KtraDoiXung (A:Mang20; N:Integer ) : Boolean;

Var Flag:Boolean;

      i :Integer;

Begin

        Flag:=True;

        For  i :=1 to N do

              If(A[i] <> A[N-i  +1]) Then

                     Flag :=False;       { Cham dut kiem tra, ket qua qua trinh : khong doi xung }

        KtraDoiXung :=Flag;

End;