Exercise 9.6 Something like a Wien bridge oscillator

See the harmonic oscillator circuit below. The circuit contains two amplifiers, one with voltage gain A and the other with voltage gain equal to 1.

a)

Derive an expression for the oscillation (angular) frequency of this oscillator, expressed in e.g. A, $C_1$, $C_2$, $R_1$, and $R_2$.

b)

Derive the value for the voltage gain A required for harmonic oscillation, expressed in e.g. $C_1$, $C_2$, $R_1$, and $R_2$.