According to Bühler, Brahmi added symbols for certain sounds not found in Semitic languages, and either deleted or repurposed symbols for Aramaic sounds not found in Prakrit. For example, Aramaic lacks the phonetic retroflex feature that appears among Prakrit dental stops, such as ḍ, and in Brahmi the symbols of the retroflex and non-retroflex consonants are graphically very similar, as if both had been derived from a single prototype. (See Tibetan alphabet for a similar later development.)