The Tenant of Wildfell Hall the book title acted out by Lady Mary Crawley in the Christmas charade. The story of Helen Graham is mentioned in Elizabeth George's 1988 novel "A Great Deliverance". Her name is also used as a secret code. Tina Connolly's 2013 novel "Copperhead" was inspired by "The Tenant of Wildfell Hall". The name of the heroine is Helen Huntingdon and she also has a disastrous marriage. Sam Baker's 2016 novel "The Woman Who Ran" takes inspiration from radical themes of Anne's novel. The heroine is a woman also called Helen, who she hides from her past (in an abusive marriage) in
19th century in science later in the 19th century by the German mathematician Bernhard Riemann; here no parallel can be found and the angles in a triangle add up to more than 180°. Riemann also developed Riemannian geometry, which unifies and vastly generalizes the three types of geometry. The 19th century saw the beginning of a great deal of abstract algebra. Hermann Grassmann in Germany gave a first version of vector spaces, William Rowan Hamilton in Ireland developed noncommutative algebra. The British mathematician George Boole devised an algebra that soon evolved into what is now called Boolean algebra, in which the only numbers were