prerm is in libtachyon-mt-0-dev 0.99~b6+dsx-4.
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 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38  | #!/bin/sh
set -e
refresh_libvariant_alternative () {
	local libvariant=$1
	local libpriority=$2
	update-alternatives --quiet \
		--install \
			/usr/lib/x86_64-linux-gnu/libtachyon.so.0 \
			libtachyon.so.0 \
			/usr/lib/x86_64-linux-gnu/libtachyon-${libvariant}.so.0 $libpriority \
		--slave /usr/lib/x86_64-linux-gnu/libtachyon.so.0.0.0 \
			libtachyon.so.0.0.0 \
			/usr/lib/x86_64-linux-gnu/libtachyon-${libvariant}.so.0.0.0
	return 0
	}
case $1 in
	remove|deconfigure)
		for LIBVARIANT in mt-openmp mt-thr; do
			case $LIBVARIANT in
			serial)         LIBPRIORITY=10 ;;
			mt-openmp)      LIBPRIORITY=110 ;;
			mt-thr)         LIBPRIORITY=150 ;;
			mpich-openmp)   LIBPRIORITY=210 ;;
			mpich-thr)      LIBPRIORITY=250 ;;
			mpich)          LIBPRIORITY=290 ;;
			openmpi-openmp) LIBPRIORITY=310 ;;
			openmpi-thr)    LIBPRIORITY=350 ;;
			openmpi)        LIBPRIORITY=390 ;;
				*) echo "unknown library variant \'${LIBVARIANT}': skip" >&2 ;;
			esac
			refresh_libvariant_alternative $LIBVARIANT $LIBPRIORITY
		done
		;;
	upgrade|failed-upgrade) ;;
	*) echo "prerm called with unknown argument \`$1'" >&2 ; exit 0 ;;
esac
exit 0
 |