# c space

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In the mathematical field of functional analysis, the space denoted by c is the vector space of all convergent sequences (xn) of real numbers or complex numbers. When equipped with the uniform norm:

${\displaystyle \|x\|_{\infty }=\sup _{n}|x_{n}|}$

the space c becomes a Banach space. It is a closed linear subspace of the space of bounded sequences, , and contains as a closed subspace the Banach space c0 of sequences converging to zero. The dual of c is isometrically isomorphic to ℓ1, as is that of c0. In particular, neither c nor c0 is reflexive.

In the first case, the isomorphism of ℓ1 with c* is given as follows. If (x0,x1,...) ∈ ℓ1, then the pairing with an element (y1,y2,...) in c is given by

${\displaystyle x_{0}\lim _{n\to \infty }y_{n}+\sum _{i=1}^{\infty }x_{i}y_{i}.}$

This is the Riesz representation theorem on the ordinal ω.

For c0, the pairing between (xi) in ℓ1 and (yi) in c0 is given by

${\displaystyle \sum _{i=0}^{\infty }x_{i}y_{i}.}$

## References

• Dunford, N.; Schwartz, J.T. (1958), Linear operators, Part I, Wiley-Interscience.