A game {$(\Omega,\Gamma,\lambda)$} in competitive on-line prediction is {$\eta$}-mixable, where {$\eta > 0$} if there exists a substitution function for it. Or if {$\forall \gamma_1,\gamma_2 \in \Gamma, \alpha \in [0,1], \exists \delta \in \Gamma$} such as {$\forall \omega \in \Omega:$}
{$\exp(-\eta\lambda(\omega,\delta)) \ge \alpha\exp(-\eta\lambda(\omega,\gamma_1)) + (1-\alpha)\exp(-\eta\lambda(\omega,\gamma_2))$}.