Suppose you wish to minimize the size of closures in a language implementation that uses a display to access nonlocal objects. Assuming a language like Pascal or Ada, in which subroutines have limited extent, explain how an appropriate display for a formal subroutine can be calculated when that routine is finally called, starting with only (1) the value of the frame pointer, saved in the closure at the time that the closure was created, (2) the subroutine return addresses found in the stack at the time the formal subroutine is finally called, and (3) static tables created by the compiler. How costly is your scheme?