Types of nodes in the ATMS
true nodes:they hold in the empty environment; they represent true facts in the domain and they belong to each environment; their number grows monotonically.
IN nodes: in their label there is at least a non-empty environment; these nodes hold if some assumptions are made and thank to the known justifications; as problem solving proceeds the environment in their label could (possibly) become inconsistent. Their
OUT nodes: their label is empty: they hold in no known consistent context. As problem solving proceeds, new contexts may be discovered, which allow OUT nodes to become IN, and viceversa.
false nodes: they do not hold in any possible context. Their number grows monotonically.