Coproducts of Ideal Monads

The question of how to combine monads arises naturally in many areas with much recent interest focusing on the coproduct of two monads. In general, the coproduct of arbitrary monads does not always exist. Although a rather general construction was given by Kelly [15], its generality is reflected in its complexity which limits the applicability of this construction. Following our own research [19], and that of Hyland, Plotkin and Power [12], we are looking for specific situations when simpler constructions are available. This paper uses fixed points to give a simple construction of the coproduct of two ideal monads. 1991 Mathematics Subject Classification. 08B20,18C15,18C50,68Q55.