Diagrammatic Reasoning About Linked Lists

A recently developed theory of local reasoning with diagrams is applied to a practical domain, that of inserting a node into a singly linked list, to illustrate its explanatory power. Prior to this demonstration there was only an informal feel as to why diagrams used to explain the generation of imperative code for similar applications should work. This paper is a partial answer to the charge that theory in artiicial intelligence is remote from application. On the contrary, it shows that properly constrained theories can assist in underpinning cognitive tools.