Code:
/dev/loop0        101376   101376         0 100% /snap/core/11081
/dev/loop1         32896    32896         0 100% /snap/snapd/11841
/dev/loop2         32896    32896         0 100% /snap/snapd/12057
/dev/loop3        101632   101632         0 100% /snap/core/11167
/dev/sda1         523248        4    523244   1% /boot/efi
tmpfs             402964      336    402628   1% /run/user/1000
ubu@ubu:~$ snap remove snapd
error: cannot remove "snapd": snap "snapd" is not removable: remove all other snaps first
ubu@ubu:~$ snap remove core
error: cannot remove "core": snap "core" is not removable: snap is used by the model
ubu@ubu:~$ sudo rm snapd
[sudo] password for ubu: 
rm: cannot remove 'snapd': No such file or directory
ubu@ubu:~$ sudo rm snap
rm: cannot remove 'snap': No such file or director
I cannot remove the final 4 /dev/loop