Cantor–Schroeder–Bernstein quadruples for Banach spaces
Elói Medina Galego · Colloquium Mathematicum · 2008
Two Banach spaces $X$ and $Y$ are symmetrically complemented in each other if there exists a supplement of $Y$ in $X$ which is isomorphic to some supplement of $X$ in $Y$. In 1996, W. T. Gowers solved the Schroeder–Bernstein (or Cantor–Bernste