²For example, the (lower-case) German “ß” doesn’t have a unique upper-case equivalent: “ß” usually maps to “SS” (for example “groß” \(\leftrightarrow \) “GROSS”), but if that would conflict with another word, then “ß” maps to “SZ” (for example “maße” \(\leftrightarrow \) “MASZE” because there’s a different word “MASSE”). Or at least that’s the way it was prior to 1998. The 1998 revisions to German orthography removed the SZ rule, so now (post-1998) the two distinct German words “masse” (English “mass”) and “maße” (“measures”) have identical upper-case forms “MASSE”. To further complicate matters, (the German-speaking parts of) Switzerland have a slightly different orthography, which never had the SZ rule.

French provides another tricky example: In France “é” \(\leftrightarrow \) “É” and “è” \(\leftrightarrow \) “È”, whereas in (the French-speaking parts of) Canada there are no accents on upper-case letters, so “é” \(\leftrightarrow \) “E” and “è” \(\leftrightarrow \) “E”.