 The proof diagram of this concept is known as the "Epitaph of Stevinus".As noted by E. J. Dijksterhuis, Stevin's proof of the equilibrium on an inclined plane can be faulted for using perpetual motion to imply a reductio ad absurdum.Dijksterhuis says Stevin "intuitively made use of the principle of conservation of energy ... long before it was formulated explicitly."