This paper is a plea for diagonals and telescopers of rational or algebraic functions using creative telescoping. using a computer algebra experimental mathematics learn-by-examples approach. We show that diagonals of rational functions (and this is also the case with diagonals of algebraic functions) are left-invariant when one performs an infinite set of birational transformations o... https://cuttingedgecutleryco.shop/product-category/cutting-board/