- is_fast_fwd($anc->[0], $desc->[0]) or fail <<END;
-$anc->[1] ($anc->[0]) .. $desc->[1] ($desc->[0]) is not fast forward
+ is_fast_fwd($anc->[0], $desc->[0]) or
+ fail f_ <<END, $anc->[1], $anc->[0], $desc->[1], $desc->[0];
+%s (%s) .. %s (%s) is not fast forward