R $=($ $+$ a$($a $+$ c$)$b$($a $+$ b$)$c$($a $+$ b $+$ c$)).$

Draw the transition diagram for a modification of your Turing machine $($possibly using an extra tape alphabet symbol$)$ such that it decides

L$($R$),$ but replaces the first $($from left to right$)$ occurrence of b with the last

symbol of the input string. Strings that do not match R may be modified on the

tape, but must be rejected.

E$.$g$.,$ if the tape initially contains aabbabcac, then the tape should contain aacbabcac

when the machine halts in the accept state.