I have three headings

Heading 1 Heading 2 Heading 3

In some other columns i have for example

Heading 2 Heading 3
Heading 1 Heading 3
Heading 3 Heading 2

In the third column i want the third heading that is not already displayed
to be displayed. So this is the outcome

Heading 1
Heading 2
Heading 1

Any help would be great