Professor H. V. Craig (1900-1981), a firm believer in the power of invariant methods in mathematical physics, introduced extensors in 1937 as "tensors relative to the extended point transformation." Both Craig and A. Kawaguchi, another giant in the field of differential geometry, began to develop extensor theory in their independent research. Their leadership inspired many others to work on generalizations, derivations, and physical applications of extensors.
"Certain Extensor Structures in the Calculus of Variations" is a compilation of independent, unpublished research originally...