InfoPath Dev

I have a form where people will enter the department they are working in. This is a single choice item. Then they will select the departments that they would like to obtain training in. This is a multi choice item. I need some validation to make sure that they don't select the department they are currently working in as an option that they want to get training in. I tried a couple things, but I couldn't get it to work correctly and searching hasn't helped. I am probably searching for the wrong terms. I tried a formula validation =If(search[transfer dept],[current dept],false,true) but it failed on all entries. Thanks for your help

 Is this a SharePoint List? Is the form customized in InfoPath or is the validation just on the list column? I ask because your formula looks like it might be for a SharePoint column, not InfoPath. :)

 The current department is populated from a SharePoint list as well as the requesting dept. This is a list of all of the depts.The first list is a single select where the requesting dept. is a multi select.

I was trying both methods and yes that formula was a SharePoint formula but one that looked like it should work. It doesn't matter where the validation comes from.