final Matrix matrix = sheetTo == null ?
((SheetImpl)sheetFrom).getMatrix() : ((BookImpl)sheetFrom.getBook()).getMatrix();
return matrix.getRef(sheetFrom, sheetTo, left, top, right, bottom);
}
public Reference removeRef(Sheet sheetFrom, Sheet sheetTo, int left, int top, int right, int bottom) {
final Matrix matrix = sheetTo == null ?
((SheetImpl)sheetFrom).getMatrix() : ((BookImpl)sheetFrom.getBook()).getMatrix();
final Reference ref = matrix.removeRef(sheetFrom, sheetTo, left, top, right, bottom);
return ref;
}