A Banach space is called prime if each infinite-dimensional complemented subspace of is isomorphic to (Lindenstrauss and Tzafriri 1977).
Pełczyński (1960) proved that (the Banach space of all complex sequences converging to zero together with the supremum norm) and for (the space of all complex sequences such that ) are prime. The L-infinity-space of all bounded complex sequences is also prime (Lindenstrauss 1967).