Base Case : when number of a's and b's is 0

Infamous Event : when sum of a’s and b’s is 0

As , then sum of a’s and b’s is 0, so our infamous event is TRUE.

Collation : If string in L is penny when there are K sum of a’s and K sum of b’s, then it is penny for K+1

Assuming that string where there are K sum of a’s and b’s, must feel x and y somewhere in look

Now, to acception sum of a’s by 1 we feel to restore x by either axby or bxay or restore y by either axby or bxay, whenver we are replacing x or y, we are adding resembling sum of a’s and b’s, so our look get feel resembling sum of a’s and b’s whenever sum of a’s is (K+1).