Abstract: A computer architecture supports reasoning tasks involving information represented in graphical form. The architecture supports the creation, storing, display, and editing of a partially ordered set of nodes representing the steps in a reasoning process, as well as representations of information associated with the nodes. Modifications are constrained by rules that support the creation of valid reasoning. In particular, special rules of inheritance place constraints upon what information is available for display and modification at any given point in the reasoning process. The present architecture supports reasoning about any type of graphical representation and about multiple representations within a single reasoning process. In addition, the present architecture supports extensible representations, i.e., representations that may be edited at later points in a proof to extend the range of possible values which may be assigned to their attributes, or to add or delete objects or attributes.