+.IP o 2
+In merging, the input files are required to have the same number of
+reference sequences. The requirement can be relaxed. In addition,
+merging does not reconstruct the header dictionaries
+automatically. Endusers have to provide the correct header. Picard is
+better at merging.
+.IP o 2
+Samtools' rmdup does not work for single-end data and does not remove
+duplicates across chromosomes. Picard is better.