4. (10pt) Recall the buffer ADT, buffer.h and suppose we consider its implementation based on the circular double link list (CDLL) representation. ForA B C. it can be visualized as follows tart cursor buffer You are asked to implement the following function which removes ALL the characters BEFORE t cursor. If the cursor is at the beginning of the buffer, then there is nothing to remove. After calling this function for the above case, the buffer will have: I B C. if the buffer had A B CD EFG, then after calling your function, it would have: IEF G