The points P=(a,b) and Q=(c,d) are in the first quadrant of the xy plane, and a,b,c and d are integers satisfying a<b,a<c,b<d and c<d. A route from point P to point Q is a broken line consisting of unit steps in the directions of the positive coordinate axes. An allowed route is a route not touching the line x=y. Tetermine the number of allowed routes. combinatoricscoordinateslattice pointsbroken line