The kings prblems in semicomplete digraphs without vertices whose in-degree are zero and locally semicomplete digraph under some conditions are discussed chiefly in the paper.
On condition that the front body shape of the projectile is unchangeable,a formula is obtained for determining the relation between the optimum boattail angle and the supersonic flight region.
Take 10 golden triangles, arrange them with their sharp points touching, and you have a golden decagon, fitting perfectly within the iris of the eye, vertices neatly touching the rim.