  VHPOP is a partial order causal link (POCL) planner loosely based on UCPOP.
It draws from the experience gained in the early to mid 1990's on flaw
selection strategies for POCL planning, and combines this with more recent
developments in the field of domain independent planning such as distance based
heuristics and reachability analysis. We present an adaptation of the additive
heuristic for plan space planning, and modify it to account for possible reuse
of existing actions in a plan. We also propose a large set of novel flaw
selection strategies, and show how these can help us solve more problems than
previously possible by POCL planners. VHPOP also supports planning with
durative actions by incorporating standard techniques for temporal constraint
reasoning. We demonstrate that the same heuristic techniques used to boost the
performance of classical POCL planning can be effective in domains with
durative actions as well. The result is a versatile heuristic POCL planner
competitive with established CSP-based and heuristic state space planners.
