text: NAME       group
  
  MODE       COMPLETION
  
  SORTS	ANY
  
  SIGNATURE
  	e : -> ANY
  	i : ANY -> ANY
  	f : ANY ANY -> ANY
  
  ORDERING   KBO
          i = 1, f = 1, e = 1
  	i > f > e
  
  VARIABLES
  	x,y,z : ANY
  
  EQUATIONS
  	f(x,e) = x
  	f(x,i(x)) = e
  	f(f(x,y),z) = f(x,f(y,z))
  	f(x,y) = f(y,x)
  
  CONCLUSION 
  