How can I make a formula in one cell, to check in a list of products if there
is any double information. Like if there is twice "Eggs" in the list?

I made already next to each cell lets say in B2 and on this formula
SUMPRODUCT(LEN($A$26:$A$33)-LEN(SUBSTITUTE(LOWER($A$26:$A$33),D27,"")))/LEN(D27))
and in C2 I put in
=A1
And then in a different place I put in
=IF(SUM(C26:C30)-COUNT(C26:C30)0,"''You entered a product twice''","")

But I want to do this all in one cell, is there a way to do this in one cell?