guard-splitting for chain(-prev), bfs(-prev) and par(-prev)
Revert "Temporary workaround for bug with regrouping combined with lddmc."

This reverts commit 09ab1d49e4715706541bccf2c679d5a8fe41ed24.
add parenthesis
make top_lvl clearer to read
don't use guard-splitting with sat-fix and sat
use correct name for dst in vset_update
add parallel enumeration
add soundness check for guard-splitting