Consider a problem of testing hypotheses in which the following hypotheses about an arbitrary parameter are

Consider a problem of testing hypotheses in which the following hypotheses about an arbitrary parameter θ are to be tested:
H0: θ ∈ Ω0,
H1: θ ∈ Ω1.
Suppose that δ is a test procedure of size α (0 < α < 1) based on some vector of observations X, and let π(θ|δ) denote the power function of δ. Show that if δ is unbiased, then π(θ|δ) ≥ α at every point θ ∈ Ω1.