Hendrik Lenstraborn 1949
Droste transform
Dutch mathematician who, with Bart de Smit, identified the conformal map hiding at the centre of Escher's Print Gallery and completed the picture.
Conformal Spiral
A square grid pushed through the exponential map. Angles survive the journey intact, so every crossing stays square while the whole sheet winds into a spiral that never quite arrives.
About this pattern
The exponential map · Lenstra and de Smit, 2003
Under w = e^z, vertical lines become circles and horizontal ones become rays. Tilt the grid before the map and both families come out as logarithmic spirals that still meet at right angles, because the map is conformal: it may stretch a shape but it cannot shear one. Lenstra and de Smit used the same transform in 2003 to work out what belongs in the blank patch at the middle of Escher's Print Gallery, and to fill it in.
Behind the mathematics
Bart de Smit
Escher and the Droste effect
Dutch mathematician who co-led the Escher and the Droste effect project, working out the exponential twist that closes the loop in Print Gallery.