diff --git a/m1r4/dsv/bomshelf b/m1r4/dsv/bomshelf
index 1bbdefe..f06c348 100755
--- a/m1r4/dsv/bomshelf
+++ b/m1r4/dsv/bomshelf
@@ -23,6 +23,29 @@ sub csv
 	
 }
 
+
+sub lookup
+{
+	my $p = $_[0];
+	my $add = $_[1];
+	my @a;
+
+	return $p if defined $cr{$p};
+	@a = grep { $_ =~ /^$p/ } keys %cr;
+	die "key $p* is ambiguous" if scalar @a > 1;
+	if (!@a) {
+		@a = grep { $_ =~ /$p/ } keys %cr;
+		die "key *$p* is ambiguous" if scalar @a > 1;
+		if (!@a) {
+			die "key $p matches nothing" unless $add;
+			warn "adding $p as supplement";
+			return $p;
+		}
+	}
+	return $a[0];
+}
+
+
 while (<>) {
 	chop;
 	@f = &csv($_);
@@ -43,6 +66,15 @@ while (<F>) {
 	chop;
 	next if /^\s*#/;
 	next if /^\s*$/;
+	if (/^[Xx]:\s*/) {
+		$p = &lookup($', 0);
+		delete $cr{$p}, $url{$p}, $dsc{$p};
+		for (keys %r) {
+			delete $r{$_} if $r{$_} eq $p;
+		}
+		undef $p;
+		next;
+	}
 	if (/^[Cc]:\s*/) {
 		undef $p if $clear;
 		$clear = 0;
@@ -60,20 +92,8 @@ while (<F>) {
 		next;
 	}
 	if (/^[Pp]:\s*/) {
-		$p = $';
+		$p = &lookup($', 1);
 		$clear = 0;
-		next if defined $cr{$p};
-		@a = grep { $_ =~ /^$p/ } keys %cr;
-		die "key $p* is ambiguous" if scalar @a > 1;
-		if (!@a) {
-			@a = grep { $_ =~ /$p/ } keys %cr;
-			die "key *$p* is ambiguous" if scalar @a > 1;
-			if (!@a) {
-				warn "adding $p as supplement";
-				next;
-			}
-		}
-		$p = $a[0];
 		next;
 	}
 	if (/^[Aa]:\s*/) {