module dec4 {
     input   in<4> ;
     output  out<4> ;
     instrin do ;
     instruct do out =  ( in<3> @ ^( /|in<2:0> ))
                     || ( in<2> @ ^( /|in<1:0> ))
                     || ( in<1> @ ^in<0> )
                     || ( ^in<0> ) ;
}