This function is the cumulative summation of the Kronecker delta:
ð ɪ s WORD_BOUNDARY f ʌ ŋ k ʃ ə n WORD_BOUNDARY ɪ z WORD_BOUNDARY ð ə WORD_BOUNDARY k j uː m j ʊ l ə t ɪ v WORD_BOUNDARY s ʌ m eɪ ʃ ə n WORD_BOUNDARY ʌ v ð ə WORD_BOUNDARY k ɹ oʊ ŋ k ə ɹ WORD_BOUNDARY d ɛ l t ə WORD_BOUNDARY