argment number check inconsistent with its function

When trying to use split command in fatt edit following message was obtained:

ERROR: # of the argument is invalid.
usage: split <sequence name> <split position (0-origin)> <left sequence name> <right sequence name>
The base at the split position goes to the right sequence.

It appears just a simple error. That the code checks the number of argument to be 3 rather than 4.