The subjects of a-nodes and c-nodes are comprehensively and exclusively defined by this RM4TM in terms of their situations in the assertions of which they are components. The properties and value-assignment rules of TM Applications are not permitted to override, obscure, add to, or fail to expose these subjects.

Perhaps close but I thing where a subject is defined is a property
of a node. Note that I removed "how" it was defined, which is a separate
issue, and one that has already been answered.