See the following source for more about Bábí letter symbolism: «Letters of the Living (Hurúf-i-Hayy)». Baháʼí Encyclopedia Project. Evanston, IL: National Spiritual Assembly of the Baháʼís of the United States. 2009.
Devin J. Steward, "The mysterious letters and other formal features of the Qur'an in light of Greek and Babylonian oracular texts", in: New Perspectives on the Qur'an ed. Reynolds, Routledge (2012), 323–348 (p. 341).