anchor.diff:  
     ###### implementation
   
  -  config = mkIf config.services.rpcbind.enable {
  +  config = mkIf config.services.rpcbind.enable (check {
   
       environment.systemPackages = [ pkgs.rpcbind ];
   
  
positive.code:         serviceConfig.ExecStart = "@${pkgs.rpcbind}/bin/rpcbind rpcbind";
        };
  
    };
  
  }
  
negative.code:     '';
    };
  
    check = mkAssert (!(config.services.rpcbind.enable && config.services.portmap.enable))
      "Portmap and rpcbind cannot both be enabled.";
  
  in
  
  