I am looking for a way to find out whether a certain string does NOT appear
in another string.
In that case FIND will give an error.

I tried to bypass this by using NOT(ISERROR(...), but this doen't seem to
work.

I tried using NOT(ISERROR(FIND("10";$BG20;1)<0 to check if "10" is prsent
in BG20
in this formula :
=IF(AND( condition 1; condition 2);
IF( $BG$1="M"; $BG20;
IF( AND($BG$1="K";
NOT(ISERROR(FIND("10";$BG20;1))));
$BG20;
IF( AND($BG$1="J";
NOT(ISERROR(FIND("10";$BG20;1))));
$BG20)));
""
)
but for BG1 = "M", I still get "FALSE" instaed of an empty field.

What am I doing wrong ?
Tx in advance,
Gilbert