The Art of Arabic Calligraphy

Fig. 2.1. Several letters in the Arabic alphabet share the same shape, and are differentiated only by the number and placement of dots on the letters.
Of the basic 18 shapes, 2 are used for three letters, 6 are used for two letters, and the remaining 10 are used for one letter each.

Fig. 2.2. In addition to the basic letter forms in figure 2, there are two additional forms of letters that are needed when writing Arabic:
The first is called the Hamza (19). It is a different representation of the letter Alif (1).
The second is called Lamalif (20). It is a required ligature that combines the letters Lam (13) and Alif (1).