prerm is in tinywm 1.3-9.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15  | #!/bin/sh
set -e
Tinywm_entry="/usr/bin/tinywm"
PACKAGE="tinywm"
case "$1" in
    remove)
        #rm -rf /etc/X11/$PACKAGE
        update-alternatives --remove x-window-manager \
       	$Tinywm_entry 
	;;
    *)
        ;;
esac
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