(*
    ||M||  This file is part of HELM, an Hypertextual, Electronic        
    ||A||  Library of Mathematics, developed at the Computer Science     
    ||T||  Department, University of Bologna, Italy.                     
    ||I||                                                                
    ||T||  HELM is free software; you can redistribute it and/or         
    ||A||  modify it under the terms of the GNU General Public License   
    \   /  version 2 or (at your option) any later version.              
     \ /   This software is distributed as is, NO WARRANTY.              
      V_______________________________________________________________ *)

let sh a b =
   if a == b then a else b

let sh1 a1 a2 b1 b2 =
   if a1 == a2 then b1 else b2 (sh a1 a2)

let sh2 a1 a2 b1 b2 c1 c2 =
   if a1 == a2 && b1 == b2 then c1 else c2 (sh a1 a2) (sh b1 b2)

let eq a b = (a == b) || (a = b)