The three short vowels, https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline53.tif"/> /a/, https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline54.tif"/> /u/, and https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline55.tif"/> /i/, also have long variants. They are written by adding one of three letters after the short vowel signs. These three letters are called in Arabic https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline56.tif"/> ḥurūlu 1-maddi, 'letters of prolongation': https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/fig6_25.tif"/>