>Pretty near Borislav, the only fact is that it always create a new ...INLIST(this.cfield).... wich performs several inlist on same field giving as result that filter doesn't work, to be sure that it works the inlist(xfield must be at the same part always.
>

>lcFilter = FILTER([YourAliasHere])
>TEXT TO lcFilt NOSHOW PRETEXT 15 TEXTMERGE
>     <<lcFilter>> <<IIF(EMPTY(lcFilter),[],[ AND ])>>
>     INLIST(<<this.lcfield>>,'<<lcValue>>')
>ENDTEXT
>

O, Then:

lcFilter = FILTER([YourAlias])
IF ATC([INLIST(]+this.lcfield, lcFilter) > 0
   lcFilter = STRTRAN(lcFilter, STREXTRACT(lcFilter,[INLIST(]+this.lcfield,[)],1,1+4),[])
ENDIF
TEXT TO lcFilt NOSHOW PRETEXT 15 TEXTMERGE
     <<lcFilter>> <<IIF(EMPTY(lcFilter),[],[ AND ])>>
     INLIST(<<this.lcfield>>,'<<lcValue>>')
ENDTEXT
SET FILTER TO &lcFilt IN YourAlias
GO TOP IN YourAlias

not tested well