@Article{Riv77b,
  author = 	 { Ronald L. Rivest },
  title = 	 { The necessity of feedback in minimal monotone combinational circuits },
  journal = 	 { IEEE Trans. on Computers },
  OPTyear = 	 { 1977 },
  OPTmonth = 	 { June },
  date =         { 1977-06 },                  
  volume = 	 { C-26 },
  number = 	 { 6 },
  pages = 	 { 606--607 },
  doi =          { 10.1109/TC.1977.1674886 }, 
  issn =         { 0018-9340 },
  abstract =     {
        We present a specific $n$-input $2n$-output positive
        unate Boolean function which can be realized with $2n$
        two-input gates if feedback is used, but which requires
        $3n-2$ gates if feedback is not used.                  
                 },                  
}