DEF VAR cset AS CHAR EXTENT 4 INIT [
   "the,that,a",
   "frog,elephant,thing",
   "walked,treaded,grows",
   "slowly,quickly"
].

FUNCTION getAmb RETURNS CHARACTER (
   i_cwords AS CHAR,
   i_iset   AS INT
):

   DEF VAR cresult   AS CHAR.
   DEF VAR ii        AS INT.
   DEF VAR cword     AS CHAR.

   DO ii = 1 TO NUM-ENTRIES( cset [ i_iset ] ) WHILE NUM-ENTRIES( cresult, " " ) < EXTENT( cset ):

      cword = ENTRY( ii, cset[ i_iset ] ).
      IF i_cwords = "" OR
         SUBSTRING( i_cwords, LENGTH( i_cwords ), 1 ) = SUBSTRING( cword, 1, 1 )
      THEN DO:
         IF i_iset = EXTENT ( cset ) THEN
            cresult = i_cwords + " " + cword.
         ELSE
            cresult = getAmb( i_cwords + " " + cword, i_iset + 1 ).
      END.

   END.

   RETURN cresult.

END FUNCTION. /* getAmb */


MESSAGE getAmb( "", 1 ) VIEW-AS ALERT-BOX.