In other words, he would like to know if a situation is not of a certain type and then use this knowledge. This calls for negation in both query statements and constraints. Note that negated forms of infons in propositions with are the assumptions. They are accepted to be true by default, unless otherwise stated. The other aspect is that of the chaining mechanism.
ASTL constraints are all in the form of backward-chaining constraints.
The user can only issue queries. However, an intelligent agent has the ability to not only acquire information about situations and obtain new information about them by being attuned to assorted constraints, but also act accordingly to alter its environment. Thus, having forward-chaining constraints as well would be better. In this way, new situations would be created, new infons would be inserted into situations, and consequences of new infons would be observed. ASTL provides a simple user interface.