What I'm trying to achieve is simple:

=IF((INDEX(INDIRECT(Tab!$C$8&"!"&Tab!$C$8&"Table23"),3,2))="Y" or "Yes"
If I leave it as ="Y" it works.
If I leave it as ="Yes" it works.
If I try =or("Y","Yes") it doesn't work.

Any clues appreciated.

Adri