The point-line geometry known as a partial quadrangle (introduced by Cameron in 1975) has the property that for every point/line non-incident pair (P, `), there is at most one line through P concurrent with `. So in particular, the well-studied objects known as generalised quadrangles are each partial quadrangles. An intriguing set of a generalised quadrangle is a set of points which induces an...

An algorithm is given for finding the minimum weight extension of a prefix code. The algorithm runs in 0(n3), where n is the number of codewords to be added, and works for arbitrary alphabets. For binary alphabets the running time is reduced to O(n*), by using the fact that a certain cost matrix satisfies the quadrangle inequality. The quadrangle inequality is shown not to hold for alphabets of...

In this article some new results are presented about planar quadrangle quality measures. On the one hand, a modi cation of the triangle quality measure based on the Frobenius norm is proposed, in order to comply with the case where the reference element is no longer equilateral, but a right isosceles triangle. Provided this modi cation, a natural use of the Frobenius norm for quadrangular eleme...

Introduction: Significant differences exist between a digital elevation model (DEM) of the Beethoven quadrangle of Mercury, derived from Mariner 10 stereo images [1,2], the shaded relief map [3], and the image mosaic of the region. The images of the Beethoven quadrangle, located in the equatorial region (25oN to 25oS, 72oW to 144oW) of Mercury, were acquired at high sun angles by Mariner 10 [4]...

The ag-transitive automorphism groups of the Tits generalized quadrangle T 2 (O 4) are classiied up to conjugacy in Aut(T 2 (O 4)). Basing on the classii-cation, it is shown that there is no ag-transitive circular extension of T 2 (O 4) or of its dual other than those constructed in 6]. This result completes the classiication of ag-transitive extensions of T 2 (O 4) and its dual.

We show that the triangular extension of a generalized quadrangle of order (3,3) is unique. The proof depends upon certain computer calculations.