The "refutation" outlined by Pat Gunning iss not quite as conclusive as he   
would have it.  
  
His argument turns on the desire for precise measurement and for equity   
across all classes of unearned increments.  
  
The imposition of a meaningful differential betwewen improved and unimproved   
land will accomplish much, without pretending full isolation.  
  
And there is a difference between classes of rent.  Perhaps all classes   
other than land rent also require the action of the recipient to put their   
endowments to work, whereas land value increases independent of that due to   
population growth.  
  
Warren Samuels