lower.readonly:
 total 16
 -rw-r--r-- 1 root root    8 Jan 31 20:20 drei
 -rw-r--r-- 1 root root    8 Jan 31 20:20 eins
 drwxr-xr-x 2 root root 4096 Jan 31 20:20 subdir1
 -rw-r--r-- 1 root root    8 Jan 31 20:20 zwei

 merged:
 total 20
 -rw-r--r-- 1 root root    7 Jan 31 20:20 drei
 -rw-r--r-- 1 root root    8 Jan 31 20:20 eins
 drwxr-xr-x 2 root root 4096 Jan 31 20:20 subdir1
 -rw-r--r-- 1 root root    7 Jan 31 20:20 vier
 -rw-r--r-- 1 root root    8 Jan 31 20:20 zwei

 upper.writeable:
 total 8
 -rw-r--r-- 1 root root 7 Jan 31 20:20 drei
 -rw-r--r-- 1 root root 7 Jan 31 20:20 vier

 work:
 total 4
 d--------- 2 root root 4096 Jan 31 20:20 work