Give a regular description for the image of the language
L={xay∈{a,b}∗∣∣y∣=1} through the transducer represented
here.
Such transducer can be alternatively formalized as
the following set of rewrite rules:
0a→aba00b→b11a→b01b→aa1
In this alternative setting, to rewrite a word
w∈L we would start
the execution with the word
0w and proceed until obtaining a word of the form
w′0 or
w′1 (i.e., a word that cannot be rewritten any further),
where
w′ would be the generated output.
In order to get more intuition on how this transducer works, consider the word
bbaa∈L and the following execution:
- 0 bbaa
Initially, the transducer is at state 0 and it remains to read the
whole word bbaa. Moreover, no output has been produced yet.
- b 1 baa
By reading a b from state 0, the transducer has moved to state 1
and outputted b. (Equivalently, the 2nd rewrite rule has been applied.)
- b aa 1 aa
By reading a b from state 1, the transducer has moved to state 1
and outputted aa. (Equivalently, the 4th rewrite rule has been applied.)
- b aa b 0 a
By reading an a from state 1, the transducer has moved to state 0
and outputted b. (Equivalently, the 3rd rewrite rule has been applied.)
- b aa b aba 0
By reading an a from state 0, the transducer has moved to state 0
and outputted aba. (Equivalently, the 1st rewrite rule has been applied.)
Since there is no more input, the execution terminates.
Hence, the image of the word
bbaa∈L through the transducer is
baababa.