ɐ dˈiːpɚ stˈeɪtmənt ʌvðə sˌɛpɚɹˈeɪʃən pɹˈɪnsɪpəl ɪz ðætðɪ ˌɛlkjˌuːdʒˈiː kəntɹˈoʊlɚɹ ɪz stˈɪl ˈɑːptɪməl ɪn ɐ wˈaɪdɚ klˈæs ʌv pˈɑːsᵻbli nˌɑːnlˈɪnɪɹ kəntɹˈoʊlɚz.
A deeper statement of the separation principle is that the LQG controller is still optimal in a wider class of possibly nonlinear controllers.