@incollection{compref303,
   author = {Simon,HA},
   year = {1973},
   title = {The Organization of Complex Systems},
   booktitle = {Hierarchy Theory - The Challenge of Complex Systems},
   editor = {Pattee,HH},
   publisher = {Goerge Braziller},
   address = {New York},
   pages = {1-27}
}

@incollection{compref208,
   author = {Levins,RD},
   year = {1973},
   title = {The Limits of Complexity},
   booktitle = {Hierarchy Theory - The Challenge of Complex Systems},
   editor = {Pattee,HH},
   publisher = {George Braziller},
   address = {New York},
   pages = {109-127}
}