ðɛɹ kəlˌæbɚɹˈeɪʃən stˈɑːɹɾᵻd æt ðə fˈeɪməs lˈɪl kˈɑːnfɹəns ɪn nˈaɪntiːnhˈʌndɹɪd fˈɪfti sˈɛvən, wˌɛɹ bˈoʊθ wɜː pɹˈɛzənt, ænd kˈʌlmᵻnˌeɪɾᵻd ɪnðə hˈɑːɡ kˈæslɚɹ ˈæksɪəmz fɔːɹ lˈoʊkəl əbzˈɜːvəbəlz ʌv kwˈɔntəm fˈiːld θˈiəɹiz.
Their collaboration started at the famous Lille Conference in 1957, where both were present, and culminated in the Haag–Kastler axioms for local observables of quantum field theories.