Ψ(t) is the time-revolving state function,
    Ψ(t) = c₁ exp(-ι E₁/ħ t) + c₂ exp(-ι E₂/ħ t) + ...

The eigenstate of A corresponding to the eigenvalue a₁  
    |a₁〉 = α₁|E₁〉 + α₂|E₂〉

The probability of measuring the eigenvalue a₁ is
    P(a₁) = |〈a₁|Ψ(t)〉|²
          ↓ Derivation on page 71
    P(a₁) = |α₁|²|c₁|² + |α₂|²|c₂|² + Re(α₁c₁⃰α₂⃰c₂ exp(-ι (E₂-E₁)/ħ t))

The Bohy Frequency (angular frequency) of two states E₁ and E₂ is thus revealed:
    ω₂₁ = (E₂ - E₁)/ħ