Kirchberg's embedding problem asks whether every separable unital C*-algebra admits a unital
embedding into a norm ultrapower 
of the Cuntz algebra 
,
where 
is a free ultrafilter on the positive
integers. The quotient here uses operator norms
rather than a tracial seminorm.
Kirchberg's Embedding Problem
See also
Cuntz Algebra, Group C*-Algebra, Norm Ultrapower, Nuclear C*-AlgebraExplore with Wolfram|Alpha
References
Goldbring, I. and Sinclair, T. "On Kirchberg's Embedding Problem." J. Funct. Anal. 269, 155-198, 2015. https://doi.org/10.1016/j.jfa.2015.02.016.Cite this as:
Weisstein, Eric W. "Kirchberg's Embedding Problem." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/KirchbergsEmbeddingProblem.html