In set theory, the letter formula_1 is used to represent a series of infinite cardinal numbers (called beth numbers).
ɪ n WORD_BOUNDARY s ɛ t WORD_BOUNDARY θ iə ɹ i WORD_BOUNDARY ð ə WORD_BOUNDARY l ɛ t ə ɹ WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY w ʌ n WORD_BOUNDARY ɪ z WORD_BOUNDARY j uː z d WORD_BOUNDARY t ə WORD_BOUNDARY ɹ ɛ p ɹ ɪ z ɛ n t WORD_BOUNDARY ʌ WORD_BOUNDARY s ɪ ɹ i z WORD_BOUNDARY ʌ v WORD_BOUNDARY ɪ n f ɪ n ə t WORD_BOUNDARY k ɑ ɹ d ɪ n ə l WORD_BOUNDARY n ʌ m b ə ɹ z WORD_BOUNDARY k ɔ l d WORD_BOUNDARY b ɛ θ WORD_BOUNDARY n ʌ m b ə ɹ z WORD_BOUNDARY