I hope I understand your question correctly, in Persian short vowels: /e/ (ِ ), /o/ (ُ ) and /a/ (َ ) are not usually written, but the long vowels: /ā/ (ا), /ū/ (و) and /ī/ (ی) are written. here are a few example: در /dar/ (in) دار /dār/ (gallows) در /dor/ (pearl) دور /dūr/ (far) دیر /dīr/ (late سر /ser/ (secret) سیر /sir/ (garlic)