A solvable group is a GG whose reaches the after finitely many steps. Explicitly, there is an integer n0n\ge 0 such that G(n)={e}G^{(n)}=\{e\}, where

G(0)=G,G(k+1)=[G(k),G(k)].G^{(0)}=G, \qquad G^{(k+1)}=[G^{(k)},G^{(k)}].

Here [G(k),G(k)][G^{(k)},G^{(k)}] is the of G(k)G^{(k)}.

Examples
  • Every abelian group is solvable: G(1)={e}G^{(1)}=\{e\}.
  • S3S_3 is solvable.
  • (Non-example) A5A_5 is not solvable.
Equivalent characterizations

Equivalently, GG is solvable iff it has a finite whose successive quotients are .