What methods did Duke William use to form his forces and why ?
Fearnley - Sander ( 1979 ) describes Grassmann 's foundation of linear algebra as follows:Following an idea of Grassmann 's father , A1 also defined the exterior product , also called " combinatorial product " ( In German : " äußeres Produkt " or " kombinatorisches Produkt " ) , the key operation of an algebra now called exterior algebra .