KATAKANA String → Symbol (we), (e) → a (we), (ue) → b (twu), (to), (tsu) → c (macron) → α (small e), (e) → d In (Shishibori and Aoe, 1993) and (Kubota et al., 1993), they only paid attention to applying their replacement or rewrite rules to words themselves and didn't pay attention to their contexts.
they wrongly decide that " " is a variant of " ."