A new expansive but weak topological invariant is introduced and shown to have a distinguished pivotal role when logically compared with existing separation axioms in the literature. The structure of topologies, which minimally satisfy this property, is identified from both a topological and an order-theoretical point of view.

Key words: Weakly submaximal, specialisation order, duplex.
AMS (MOS) Classification: Primary 54A10, 54D10; Secondary 06A10.

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