Escher and the Droste effect. Public talk by Hendrik Lenstra, Wednesday, 14 December

In 1956, the Dutch graphic artist M.C. Escher made an unusual lithograph with the title `Print Gallery‘. It shows a young man viewing a print in an exhibition gallery. Amongst the buildings depicted on the print, he sees paradoxically the very same gallery that he is standing in. A lot is known about the way in which Escher made his lithograph. It is not nearly as well known that it contains a hidden `Droste effect‘, or infinite repetition; but this is brought to light by a mathematical analysis of the studies used by Escher. On the basis of this discovery, a team of mathematicians at Leiden produced a series of hallucinating computer animations. These show, among others, what happens inside the mysterious spot in the middle of the lithograph that Escher left blank.

Hendrik Lenstra received his doctorate from the University of Amsterdam in 1977 and became a professor there in 1978. In 1987 he was appointed to the faculty of the University of California, Berkeley; starting in 1998, he divided his time between Berkeley and the University of Leiden, until 2003, when he retired from Berkeley to take a full-time position at Leiden. He was awarded the Spinoza prize in 1998, and on 24 April 2009 he was made a Knight of the Order of the Netherlands Lion. Lenstra has worked principally in computational number theory and is well known as the discoverer of the elliptic curve factorization method and a co-discoverer of the Lenstra–Lenstra–Lovász lattice basis reduction algorithm.

Hendrik Lenstra is currently Hirzebruch Visiting Professor at the Max Planck Institute for Mathematics in Bonn.