Every node has named properties for which it may exhibit values. Some properties are "Subject Identity Discrimination Properties (SIDPs)". The values of SIDPs comprehensively and exclusively specify the subject for which the node is a proxy; SIDP values are the only basis for recognizing when two nodes have the same subject or different subjects, and should therefore either be merged or left unmerged.

Properties of nodes and use of them are inappropriate here. SIDPs
are defined separately and should not be repeated here. Just bulks up
the spec with no attending increase in clarity.