What is this symbol and what does it mean? See attachment.© BrainMass Inc. brainmass.com March 4, 2021, 5:37 pm ad1c9bdddf
Please see attachment
means union of an arbitrary number. Please see following.
Properties of open sets
1. The union (of an arbitrary number) of open sets is open.
Let x Ai = A. Then s Ai for some i. Since ...
This explains a given symbol. The expert examines topology.