Problem $7$ Let COMPLETES$\_$R in L$,$wx in R$,$ where R is some regular language. In other words, it's the language of all strings which when appended to the front of some string in L$,$ create a string in R$.$ Prove by construction on PDAs that the set of context$-$free languages is closed under COMPLETES$\_$R for all R$.$ Hint: think about what transitions we should be following when reading the input, and what to do afterwar