Maximal directed paths in the meet digraph
for independent sets of the order 4 graphs.


  1            
  2 <- 3,4     
  2 <- 4,5     
  2 <- 4,5,7   
  2 <- 4,7     
  3 <- 5,6    
  3 <- 5,6,7  
  3 <- 5,7    
  3 <- 5,7,8  
  3 <- 5,8    
  3 <- 6,7    
  3 <- 7,8    
  4           
  5           
  6 <- 8,9    
  7            
  8            
  9            
 10            
 11 <- emptyset