Using AntlrWorks, I simplified the sql select statement given in your grammar list. The grammar passes "Check Grammar" in AntlrWorks but CoCo/R warned of several ambiguities. Of course seeing the grammar would be best, but in general can anyone think of why ANTLR and CoCo/R would disagree as to the correctness of a grammar (assuming I haven't botched things). Since I am not able to understand how parsers work, a simple explanation, if possible, would be appreciated.