InfoPath Dev

Hi I was create a repeating section and drag a combo box within it. in the combo box we have some value for example A,B,C and D i want the user can not ability select same value in one selected. I mean for example Mr.Jon selected aren't A , A or B , B he can select A,C or B,C etc... what am i do?

Try this blog post - I think it may be what you are trying to achieve: http://blogs.msdn.com/b/infopath/archive/2006/08/10/694530.aspx