program exercise (input, output);

type
    ArrayType = array [1..10] of integer;

var
    list: ArrayType;
    i: integer;

procedure Trace (list: ArrayType; left, right: integer; entering: boolean);
begin
    if entering then begin
	writeln ('**** Entering mergesort:');
    end else begin
	writeln ('**** Leaving mergesort:');
    end;
    if right = left then begin
	writeln (left:3);
	writeln (list[left]:3);
    end else if right > left then begin
	write (left:3);
	for i := left+1 to right-1 do begin
	    write (' ':3);
	end;
	writeln (right:3);
	for i := left to right do begin
	    write (list[i]:3);
	end;
	writeln;
    end;
end;

procedure Merge (source: ArrayType; var destination: ArrayType;
		 index1, bound1, index2, bound2: integer);
var
    merging, i: integer;
begin
    merging := index1;
    while (index1 <= bound1) and (index2 <= bound2) do begin
	if source[index1] < source[index2] then begin
	    destination[merging] := source[index1];
	    index1 := index1 + 1;
	    merging := merging + 1;
	end else begin
	    destination[merging] := source[index2];
	    index2 := index2 + 1;
	    merging := merging + 1;
	end;
    end;
    for i := index1 to bound1 do begin
	destination[merging] := source[i];
	merging := merging + 1;
    end;
    for i := index2 to bound2 do begin
	destination[merging] := source[i];
	merging := merging + 1;
    end;
end;

procedure Mergesort (var list: ArrayType; left, right: integer);
const
    ENTERING = true;
    LEAVING = false;
var
    middle, i: integer;
    tempList: ArrayType;
begin
    Trace (list, left, right, ENTERING);
    if left < right then begin
	middle := (left+right) div 2;
	for i := left to right do begin
	    tempList[i] := list[i];
	end;
	Mergesort (tempList, left, middle);
	Mergesort (tempList, middle, right);
	Merge (list, tempList, left, middle, middle+1, right);
    end;
    Trace (list, left, right, LEAVING);
end;

begin
    write ('Please type ten numbers:  ');
    for i := 1 to 10 do begin
	read (list[i]);
    end;
    readln;
    Mergesort (list, 1, 10);
end.