when writing the code \ar @{{˜}>} I keep getting the message: "dir not
defined", so I went to the manual and saw some examples for defining tips of
arrows, and wasnt able to get it right for the shaft ~ , I already tried
other things like \ar @{{}˜>} , \ar @{{}~>} and the like, and at some point
while trying to define the ~shaft in the preamble, I got the message:
conversion failed.... thanks!
