The dutch mathematician Edsger Dijkstra (1930-2002) worked out an [url=https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm]algorithm[/url] to calculate the shortest path between two points of a graph.[br]The idea is to label the knots of the graph and to choose the smallest of them. [br]We use temporary and permanent labels. A temporary label shows the shortest distance from the starting point to the knot so far.[br]By each step this label can decrease. A temporary label of a knot is made permanent when we conclude that there is no shorter path to the knot.