Ibn al-Haytham's lemmas for solving ?Alhazen's problem?

Abstract

"Alhazen ' s p r o b l e m " , * or "problema Alhaseni (or Alhazeni)", is the name given by seventeenth-century mathemat ic ians to a p rob l em which they encounte red in the Optics of AL-HASAN IBN AL-HAYTHAM. The Optics, composed in the first ha l f o f the eleventh century, h a d been t rans la ted into La t in in the late twelf th o r ear ly th i r teenth century, 1 and an edi t ion o f it by FRIEDRICr~ RISNER had been publ i shed at Basel in 1572. 2 CHRISTIAAN t-ItJYCENS fo rmula t ed the p r o b l e m as