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The frame envelope of a $$\sigma$$-frame. (English) Zbl 0779.06009
Summary: The universal frame extension of a $$\sigma$$-frame is studied, with particular attention to constructiveness and choice principles. In particular, the $$\sigma$$-frame coproduct is related to that of frames, providing a constructively valid proof of its compactness for compact $$\sigma$$-frames. Further, a $$\sigma$$-frame is shown to consist exactly of the Lindelöf elements of its frame envelope, and some consequences of this are explored.

##### MSC:
 06D20 Heyting algebras (lattice-theoretic aspects) 54B10 Product spaces in general topology
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##### References:
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