Using the visual search method, we show that stimuli that contain curvature discontinuities (i.e., points where the second derivative along an image contour is not defined) are easily found among stimuli containing only smooth changes in curvature. Curved stimuli that lack curvature discontinuities, however, are difficult to find among distractors that have them. These results suggest that the ...

SOME systems of collineation groups which arise in connection with the theory of elliptic functions have been investigated by Klein | and HurwitzJ. One of them is a system in n variables each group of which contains an invariant subgroup of order n. For n SL prime the quotient group with respect to this invariant subgroup is (1, 1) isomorphic with the modular group on two indices of order n(n —...

Let V be a vector space of finite dimension n over a finite field GF(q). Let Lk(V ) denote the set of k-dimensional subspaces of V. Several authors have studied groups acting on Lk(V ) for various k. Wagner [9] considered groups which act doubly transitively on LI(V ). Recently Kantor [6] has shown that most groups which act transitively on L2(V) also act doubly transitively on LI(V ). This pap...

From the Introduction to P. Dembowski’s Finite Geometries, Springer, Berlin 1968: “ . . . An alternative approach to the study of projective planes began with a paper by BAER 1942 in which the close relationship between Desargues’ theorem and the existence of central collineations was pointed out. Baer’s notion of (p, L)–transitivity, corresponding to this relationship, proved to be extremely f...