# Goal: Turn
#
# A -> B C
# A -> B D
# A -> B C D
# A -> B D C
# A -> C B
# B -> B E
# B -> B E C D
#
# into
#
# A -> B C
# A -> C B
# -
# A -> B D
# -
# A -> B C D
# A -> B D C
# -
# B -> B E
# -
# B -> B E C D
#
# Both the order of the groups and the order of rules within each
# group are irrelevant.
#
# Idea: Do this for each lhs: as we read each line, sort its rhs and
# use that sort as the key for a listhash (i.e. each key maps to a
# list of values). At the end, for each key in the hash, print out its
# list of values followed by the delimiter.

$curlhs = "";
$first = 1;

while (<>) {
    if (m/=>/) {
	print;
	next;
    }
    ($lhs, $rhs) = m/(.*) -> (.*)/;
    if (!$first && ($lhs ne $curlhs)) {
	@values = values(%map);
	while (@values) {
	    @curlist = pop(@values);
	    while (@curlist) {
		print @{pop(@curlist)};
	    }
	    print "-\n";
	}
	%map = ();
    }
    $curlhs = $lhs;
    $first = 0;
    @rhslist = split(" ", $rhs);
    @srhslist = sort(@rhslist);
    $srhs = join(" ", @srhslist);
    push(@{$map{$srhs}}, $_);
}

@values = values(%map);
while (@values) {
    @curlist = pop(@values);
    while (@curlist) {
	print @{pop(@curlist)};
    }
    print "-\n";
}
%map = ();