A 1‐separably injective Banach space that does not contain ℓ∞
A 1‐separably injective Banach space that does not contain ℓ∞
We show that the problem whether every 1-separably injective Banach space contains an isomorphic copy of ℓ ∞ is undecidable. Namely, unlike under the continuum hypothesis, assuming Martin's axiom and the negation of the continuum hypothesis, there is an 1-separably injective Banach space of the form C ( K ) …