|I set up Sheet 1 like this:|
1 1 =SHEET2!A1
2 2 =SHEET2!A2
I set up Sheet 2 like this:
1 3 =SHEET1!A1
2 4 =SHEET1!A2
I then selected Columns A:B on Sheet 1 and applied Mike's Data Validation suggestion as follows:
I then selected Columns A:B on Sheet 2 and applied Mike's Data Validation suggestion in the same manner:
I then hid Column B on both sheets.
Any value entered in Column A of either sheet is checked against both columns on that sheet and duplicates are prohibited.
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