If the system is a three state system (for example, three species of neutrinos ν e ⇄ ν μ ⇄ ν τ, three species of quarks d ⇄ s ⇄ b ), then, just like in the two state system, the flavor eigenstates (say | φ φ α α ⟩ , | φ φ β β ⟩ , | φ φ γ γ ⟩ ) are written as a linear combination of the energy (mass) eigenstates (say | ψ ψ 1 ⟩ , | ψ ψ 2 ⟩ , | ψ ψ 3 ⟩ ). That is,