Hi Sayan,
For IN you can use like this, but pay special attention to nulls if your COL1 can contain it:
var_out = CE_PROJECTION (:v1, ["COL1", "COL2"], ' in("COL1",''A'',''B'',''C'') ');
Regards, Fernando Da Rós
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Observation: Do performance tests on IN versus OR uses. Last time I used in, around rev18, it had difference in performance which sometimes OR was faster. Not tested since than.