Three teachers x1, x2, x3 teach four classes y1, y2, y3, y4

Three teachers x1, x2, x3 teach four classes y1, y2, y3, y4 for these numbers of periods:

Show that this arrangement can be represented by a bipartite graph G and that a teaching schedule for one period corresponds to a matching in G. Set up a teaching schedule with the smallest possible number of periods.

PROBLEM SET 23.3: