Topological sorting is an algorithm that takes a graph consisting of nodes and other nodes that depend on them, forming a partial order, and returns a list representing a total ordering of the graph. If the graph is cyclic, the topological sort will fail. The procedure topological-sort returns three values. If sorting succeeds, the first value contains the result and the second and third are #false. If sorting fails, the result is #false and the second and third value may provide additional information about the error.