Quite a basic query I think ...
If the data in column F, finds a matching cell in column A of Sheet 1, write a "yes", if not write a "no" . This is what I have at the moment:
=IF(VLOOKUP(F10,Sheet1!A:A,1,FALSE)=F10,"yes","no")
It returns "yes" for a match, but returns "n/a" if there's no...