# Shorten the grammar by lifting modification
#
# Test case:
#
# A:OB -> B:OB C:OB D:OB
# A:OB -> E:OP F:OB G:OB
# A:OB -> H:OP I:OB J:OP
#
# becomes
#
# A:OB -> B:OB C:OB D:OB
# A:OB -> F:OB G:OB
# A:OB => A:OB E:OP
# A:OB -> I:OB
# A:OB => A:OB H:OP
# A:OB => A:OB J:OP
#
# where OP is optional and OB is obligatory
#
# (the => arrow insulates a rule from order generalization)

while (<>) {
    @oplist = ();
    @oblist = ();
    ($lhs, $rhs) = m/(.*) -> (.*)/;
    @rhslist = split(" ", $rhs);
    foreach $item (@rhslist) {
	if ($item =~ m/:AMS|:APP|:CC|:DM|:GR|:MNR|:MO|:NG|:PG|:RC|:SBP|:VO|AA:NK|AP:NK|AVP:NK|CAP:NK|CAVP:NK|MTA:NK|CPP:NK|PP:NK/) {
	    push @oplist, $item;
	} else {
	    push @oblist, $item;
	}
    }
    $newrhs = join " ", @oblist;
    print "$lhs -> $newrhs\n";
    foreach $item (@oplist) {
	print "$lhs => $item $lhs\n";
    }
}