Arabic definite and indefinite

Like English, Arabic nouns can be indefinite ( نَكِرَةٌ ) or definite (مَعْرِفَةٌ)
An indefinite noun is indicated by تَنْوِيْنٌ, which doubles the vowel sign at the end
of the word, e.g.
A book – كِتَا بٌ
A chair – كرْسِيٌ
A Definite noun is indicated by اَلْ prefixed to the noun. This also results in
eliminating the تَنْوِيْنٌ at the end of the word, e.g.
The book – اَلْكِتَا بٌ
The chair – اَلْكرْسِيٌ
اَلْ and تَنْوِيْنٌ cannot coexist. So اَلْكِتَا بٌ will be incorrect
Please note many proper nouns, e.g. محَمَّدٌ, خَالِدٌ end with تَنْوِيْنٌ , but they are still