新手求救！！！关于mapbasic的

本人最近自学mapbasic，遇到一个问题：如果用a.mb中的main，调用b.mb中的sub，要如何才能实现？请高手明示！
a.mb内容为：
Include "mapbasic.def"
Declare Sub Main


<P> Sub Main
  print "In Main"
  print Chr$(32)
  Call Sub pro2
 End Sub</P>
<P>b.mb内容为：
Include "mapbasic.def"
Declare Sub pro2</P>
<P> Sub pro2
  print "In Sub"
 End Sub
 
 热切期待答复！谢谢！！！</P>

a.mb内容为：
Include "mapbasic.def"
Declare Sub Main
Declare Sub pro2


<P>Sub Main
  print "In Main"
  print Chr$(32)
  Call Sub pro2
End Sub</P>
<P>b.mb内容为：
Include "mapbasic.def"
Declare Sub pro2
Declare Sub Main </P>
<P>Sub pro2
  print "In Sub"
End Sub
</P>