Covariantly Adjusting Co-Types in Timor

This paper extends the idea of co-types (described in a companion paper) to include the concept of adjustment hierarchies. An adjustment hierarchy provides a parallel hierarchy to a subtyping hierarchy of a type being expanded by the co-type. This has a number of advantages including the predefinition of co-types for subtypes of an expanded type, and allowing automatic covariant adjustment of parameters for makers, binary methods and instance methods, without creating problems for static type safety.