Let T 1 be a transducer that maps between regular languages U 1 and L 1 , and let T 2 be a transducer that maps between regular languages U 2 and L 2 .
the composition t of t 1 and t 2 , denoted by t 1 • t 2 , is the transducer that maps between the resulting mapping is defined only for the respective images, in t −1 Note that the composition operation is order dependent; t 1 • t 2 is not the same mapping as t 2 • t 1 .