> In 1926 O Veblen and J M Thomas [in Projective invariants of affine geometry of paths, Ann. of Math. 27 (1926), 278-296] defined an "invariant" in the following way:
"An invariant ... is an entity with definite determining components in any coordinate system, such that the transformations of the components from one coordinate system to another form a group, isomorphic with the group of analytic transformations of the coordinates".
In 1927 O Veblen [Invariants of quadratic differential forms, Cambridge Tracts, No. 24 (1927), 14] gave the definition: