bool backward_chain()
{
int act_cost = m_Candidates.Keys.Min();
var cache = m_Candidates[act_cost];
var working = new List <Actions.ActionChain>();
int ub = cache.Count;
while (0 <= --ub)
{
var dest = cache[ub];
var setup = CanBackwardPlan(dest);
if (null == setup)
{
throw new ArgumentNullException(nameof(setup)); // invariant failure
}
foreach (var x in setup)
{
var test = new Actions.ActionChain(x, dest);
if (!test.IsSemanticParadox())
{
working.Add(test);
}
}
cache.RemoveAt(ub);
if (0 >= working.Count)
{
continue;
}
foreach (var chain in working)
{
splice(chain);
}
return(true);
}
return(false);
}
