ɪf ɪz ɐ dˈɪfɚɹˌɛnʃɪəbəl fˈʌŋkʃən fɹʌm sˌʌm ˈoʊpən sˈʌbsɛt tʊ ænd ɪz ɐ dˈɪfɚɹˌɛnʃɪəbəl fˈʌŋkʃən fɹʌm sˌʌm klˈoʊzd ˈɪntɚvəl tʊ nˈoʊt ðæt ɪz dˈɪfɚɹˌɛnʃɪəbəl æt ðɪ ˈɪntɚvəl ɛndpˈɔɪnts ænd .
If  is a differentiable function from some open subset  to  and  is a differentiable function from some closed interval  to  (Note that  is differentiable at the interval endpoints  and .