Skip to main content
1 of 2
Pietro Majer
  • 60.6k
  • 4
  • 122
  • 269

Complemented subspaces in a dual Banach space

Let $Y$ be a complemented subspace in a dual Banach space $X$. Is it true that $Y$ is itself isomorphic to a dual?

This is the case of a $w^*$-closed subspace $Y$, but a complemented subspace of $X^*$ need not be $w^*$-closed (for instance $Z^*\subset Z^{***}$ is complemented but never $w^*$-closed unless $Z$ is reflexive). I think it is not true, but is there a simple counterexample?

Pietro Majer
  • 60.6k
  • 4
  • 122
  • 269