多线程基础问题

Question

刚刚开始接触多线程，下面是使用Delphi 7照“Delphi 6开发人员指南”上的一个例子做的,可是编译报错：[Fatal Error] Main.pas(7): Circular unit reference to 'Main'。请问这个循环的引用怎么解决呢？
源码
unit Main;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls,MyThread;type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Edit1: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
var
  NewThread:TMyThread;
begin
  NewThread:=TMyThread.Create(False);end;end.unit MyThread;interfaceuses
  Classes,Main;type
  TMyThread = class(TThread)
  private
    { Private declarations }
    Answer:Integer;
  protected
    procedure Execute; override;
    procedure GiveAnswer;
  end;implementation{ TMyThread }procedure TMyThread.GiveAnswer;
begin
  Form1.Edit1.Text:=IntToStr(Answer);
end;procedure TMyThread.Execute;
var
  i:Integer;
begin
  { Place thread code here }
  FreeOnTerminate:=true;
  for i:=i to 2000000 do
    begin
      if Terminated then break;
      inc(Answer,Round(Abs(Sin(Sqrt(i)))));
      Synchronize(GiveAnswer);
    end;
end;end.

Answer 1

unit MyThread;interfaceuses
  Classes;type
  TMyThread = class(TThread)
  private
    { Private declarations }
    Answer:Integer;
  protected
    procedure Execute; override;
    procedure GiveAnswer;
  end;implementation
uses
  Main;{ TMyThread }procedure TMyThread.GiveAnswer;
begin
  Form1.Edit1.Text:=IntToStr(Answer);
end;procedure TMyThread.Execute;
var
  i:Integer;
begin
  { Place thread code here }
  FreeOnTerminate:=true;
  for i:=i to 2000000 do
    begin
      if Terminated then break;
      inc(Answer,Round(Abs(Sin(Sqrt(i)))));
      Synchronize(GiveAnswer);
    end;
end;end.

Answer 2

将引用放在实现（impelement）而不是接口（interface）部分就可以了。—————————————————————————————————
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