4. Generate a push-down automata that accepts words on the alphabet fa, b) such that: a. The stack initially contains an unknown number of 'a' values b. The input is (a+b) c. For every. 'a' character in the input an 'a is popped from the stack and b input is ignored until (dum dum daaaaa) must be sung mysteriously. d. Once the stack is empty the 'b's are pushed to the empty stack from the input and any further 'a' values are ignored. e. After input is over, the stack is emptied. If the number of b's is even, then accept else fail Xcredit: generate a regular expression describes the accepted strings