src/HOL/Real/Hyperreal/HyperDef.thy

FreeUltrafilterNat ("\\<U>");

(*  Title       : HOL/Real/Hyperreal/HyperDef.thy
    ID          : $Id$
    Author      : Jacques D. Fleuriot
    Copyright   : 1998  University of Cambridge
    Description : Construction of hyperreals using ultrafilters
*) 

HyperDef = Filter + Real +

consts 
 
    FreeUltrafilterNat   :: nat set set    ("\\<U>")

defs

    FreeUltrafilterNat_def
    "FreeUltrafilterNat    ==   (@U. U : FreeUltrafilter (UNIV:: nat set))"


constdefs
    hyprel :: "((nat=>real)*(nat=>real)) set"
    "hyprel == {p. ? X Y. p = ((X::nat=>real),Y) & 
                   {n::nat. X(n) = Y(n)}: FreeUltrafilterNat}"

typedef hypreal = "UNIV//hyprel"   (Equiv.quotient_def)

instance
   hypreal  :: {ord, zero, plus, times, minus}

consts 

  "1hr"       :: hypreal               ("1hr")  
  "whr"       :: hypreal               ("whr")  
  "ehr"       :: hypreal               ("ehr")  


defs

  hypreal_zero_def     "0 == Abs_hypreal(hyprel^^{%n::nat. (#0::real)})"
  hypreal_one_def      "1hr == Abs_hypreal(hyprel^^{%n::nat. (#1::real)})"

  (* an infinite number = [<1,2,3,...>] *)
  omega_def   "whr == Abs_hypreal(hyprel^^{%n::nat. real_of_posnat n})"
    
  (* an infinitesimal number = [<1,1/2,1/3,...>] *)
  epsilon_def "ehr == Abs_hypreal(hyprel^^{%n::nat. rinv(real_of_posnat n)})"

  hypreal_minus_def
  "- P == Abs_hypreal(UN X: Rep_hypreal(P). hyprel^^{%n::nat. - (X n)})"

  hypreal_diff_def 
  "x - y == x + -(y::hypreal)"

constdefs

  hypreal_of_real  :: real => hypreal                 
  "hypreal_of_real r         == Abs_hypreal(hyprel^^{%n::nat. r})"
  
  hrinv       :: hypreal => hypreal
  "hrinv(P)   == Abs_hypreal(UN X: Rep_hypreal(P). 
                    hyprel^^{%n. if X n = #0 then #0 else rinv(X n)})"

  (* n::nat --> (n+1)::hypreal *)
  hypreal_of_posnat :: nat => hypreal                
  "hypreal_of_posnat n  == (hypreal_of_real(real_of_preal
                            (preal_of_prat(prat_of_pnat(pnat_of_nat n)))))"

  hypreal_of_nat :: nat => hypreal                   
  "hypreal_of_nat n      == hypreal_of_posnat n + -1hr"

defs 

  hypreal_add_def  
  "P + Q == Abs_hypreal(UN X:Rep_hypreal(P). UN Y:Rep_hypreal(Q).
                hyprel^^{%n::nat. X n + Y n})"

  hypreal_mult_def  
  "P * Q == Abs_hypreal(UN X:Rep_hypreal(P). UN Y:Rep_hypreal(Q).
                hyprel^^{%n::nat. X n * Y n})"

  hypreal_less_def
  "P < (Q::hypreal) == EX X Y. X: Rep_hypreal(P) & 
                               Y: Rep_hypreal(Q) & 
                               {n::nat. X n < Y n} : FreeUltrafilterNat"
  hypreal_le_def
  "P <= (Q::hypreal) == ~(Q < P)" 

end