This is what I tried but this doenst work:
=ISNUMBER(SEARCH($K$4:$K$7;L4))
I want to check if E4 contains the same string as K4 thru K7. Is this somehow possible? I know that this is possible: =ISNUMBER(SEARCH(K4;L4))
Try a match formula. It should be very similar to the way you're using the search formula.
=ISNUMBER(MATCH(L4,$K$4:$K$7,0))