## Abstract

In this paper we extend the high level execution language \congolog (developed at the University of Toronto) by adding to it a new construct which we call the {\em htn}-construct. The new construct improves \congolog by allowing easy specification of non-determinism when a partial ordering between a set of actions needs to be maintained. Furthermore, it allows temporal constraints to be specified easily. We present an implementation of the {\em htn}-construct in PROLOG which can be directly added to PROLOG implementations of ConGolog interpreters.