I did state that there was a problem with delete_mark.
I was stating that delete_mark was doing the function expected.
The ACL found HansBigalke with
find " HansBigalke"
The find command "marks" the found item, i.e. highlights it.
The delete_mark command deletes the "marked" item, thus HansBigalke is deleted.
Note in the video, that in the lower left corner of the Editor window is the error
"Impossible de trouver la chaine [sensible á la casse, annotation incluse]."
It seems that you are getting this error, because the commands ie are failing.
Not sure the elements cannot be inserted.