Description: Given the sum of two functions, the preimage of an unbounded below, open interval, expressed as the countable union of intersections of preimages of both functions. Proposition 121E (b) of Fremlin1 p. 37 . (Contributed by Glauco Siliprandi, 26-Jun-2021)
Ref | Expression | ||
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Hypotheses | smfaddlem1.x | |
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smfaddlem1.b | |
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smfaddlem1.d | |
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smfaddlem1.r | |
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smfaddlem1.k | |
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Assertion | smfaddlem1 | |