Hi guys

I've done almost all of assignment 2, but question 1 still has me confused. In the module it seems we only work with numbers in these cases. For example on p. 13 of the study guide the additional exercises we are supposed to do the same as Assignment Question 1 but with numbers. This is easy enough. The function, for example, is something like f(x)=x+1. However, how are we supposed to write the function with the alphabet {a,b}? In question 1 a i have the generators aba,abb,aab and bab. How am I supposed to formulate a mathematical function from this? I mean, it's supposed to be odd strings containing "ab". So do I say f(x)=x+a*b* or f(x)=x+b*a* or what?

Could someone please help me out or at least point me to a similar example somewhere in the textbook or study guide.

Thanks