Ok im a bit confused here. According to the definition of a proper subset means that everything in set A is in set b and a set always contains an extra pair of brackets. But in this example(adsbygoogle = window.adsbygoogle || []).push({});

C={∅,{∅}} why is this correct ∅ ⊆C instead of {∅} ⊆C for the first object?

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# Empty set as a subset?

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