Save the last entry and shift in decreasing index order, so no source is overwritten before being used:
PROCEDURE RightOne;
VAR saved: T; i: INTEGER;
BEGIN
  saved := a[N-1]; i := N-1;
  WHILE i > 0 DO
    a[i] := a[i-1]; i := i-1
  END;
  a[0] := saved
END RightOne;
The loop invariant is saved = A[N-1], for , and for . The decreasing loop variant is . At exit the untouched saved value fills index zero. The result is , again with reads, writes, and one extra value of type T. Applying this after part (b) restores every original entry.

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