 Several colleagues offered suggestions about earlier drafts of this entry, for which I am extremely grateful: Edward Harcourt, Lisa Bortolotti, Jeff Poland, Derek Bolton, Somogy Varga, Kelso Cratsley, John Sadler, George Graham, Alexandra Pârvan, Şerife Tekin, and Christian Perring. My special thanks for invaluable comprehensive critique are owed to Ginger Hoffman and two anonymous readers assigned by the Encyclopedia.