func (e Unorderable) Error() string {
	const maxNodes = 10
	var n int
	for _, c := range e {
		n += len(c)
	}
	if n > maxNodes {
		return fmt.Sprintf("topo: no topological ordering: %d nodes in %d cyclic components", n, len(e))
	}
	return fmt.Sprintf("topo: no topological ordering: cyclic components: %v", [][]graph.Node(e))
}
Error satisfies the error interface.
package topo
import (
	"fmt"
	"sort"
	"gonum.org/v1/gonum/graph"
	"gonum.org/v1/gonum/graph/internal/ordered"
	"gonum.org/v1/gonum/graph/internal/set"
)
type Unorderable [][]graph.Node