             log("generators:")
             log(generators.map{ "\t\($0.dim): \($0)"}.joined(separator: ",\n"))
             
-            if !relations.isEmpty {
+            if !diff.isEmpty {
                 log("")
-                log("relations:")
-                log(relations.map { "\t\($0.anyElement!.0.dim): \($0)"}.joined(separator: ",\n"))
+                log("diffs:")
+                log( diff.sorted(by: {$0.0 <= $1.0} ).map { (s, c) in "\t\(s) -> \(c)"}.joined(separator: ",\n"))
             }
             log("")
             

        return Cohomology(name: K.name, H, map, factorizer)
    }
}

    internal var debug = false
    
    internal var generators = [S]()
    internal var diff = [S : C]()

    internal var fNodes = [S : Node]()
