Proposition 3, Book XII, Euclid's Elements
This Demonstration is a dynamic illustration and a generalization of Proposition 3, Book XII of Euclids's Elements.
Proposition 3, Book XII of Euclid's Elements states: Any pyramid which has a triangular base is divided into two pyramids equal and similar to one another, similar to the whole and having triangular bases, and into two equal prisms; and the two prisms are greater than the half of the whole pyramid . ("Equal" means "have the same volume".)
The generalization includes lemma 14 .
 V. G. Boltyanskii, Tretja Problema Hilberta, Moscow: Nauka, 1977. Translated by R. A. Silverman as Hilbert's Third Problem (New York: John Wiley & Sons, Inc., 1978).  D. E. Joyce, "Euclid'sElements: Introduction."  Euclid, Elements, T. L. Heath, trans., as The Thirteen Books of Euclid’s Elements, 2nd ed., Book 3, New York: Dover Publications, 1956 pp. 378.