The "ring" diacritic used in vowels such as å likewise originated as an o-ligature. Before the replacement of the older "aa" with "å" became a practice, an "a" with another "a" on top (aͣ) could sometimes be used, for example in Johannes Bureus's, "Runa: ABC-Boken" (1611). The uo ligature ů in particular saw use in Early Modern High German, but it merged in later Germanic languages with u (e.g. MHG , ENHG "fuͦß", Modern German "foot"). It survives in Czech, where it is called .