Hey Crystal Reports Lovers!

I need a little assist on a Crystal Reports v10 formula that half works, but I cannot get the InStr portion to work with the Not(....) command.

My formula builds a concatenated string from a field in the Detail Section and shows the concatenated string in the Group Footer Section.

StringVar PO;
If {PO11.FULLY_CLOSED_FLAG} <> "C" Then
PO := PO + '   ' + {PO11.PO_NUMB};

What I really want to do is concatenate each value, but skip the concatenation of the value on the detail line, if the same exact value has already been concatenated on an earlier detail line.

I tried the following code using various configurations, but could not find a way around the syntax errors using the InStr command with Not.

StringVar PO;
If {PO11.FULLY_CLOSED_FLAG} <> "C" and
Not(InStr(PO, {PO11.PO_NUMB}) Then
PO := PO + '   ' + {PO11.PO_NUMB};

Anybody have a better idea or can you please show me what I am doing wrong?

THANK YOU VERY MUCH!!!