Theory SetUtils

Auction Theory Toolbox (

* Marco B. Caminati
* Manfred Kerber <>
* Christoph Lange <>
* Colin Rowat <>

Dually licenced under
* Creative Commons Attribution (CC-BY) 3.0
* ISC License (1-clause BSD License)
See LICENSE file for details
(Rationale for this dual licence:

section ‹Additional material that we would have expected in Set.thy›

theory SetUtils


subsection ‹Equality›

text ‹An inference (introduction) rule that combines @{thm equalityI} and @{thm subsetI} to a single step›
lemma equalitySubsetI: "(x . x  A  x  B)  (x . x  B  x  A)  A = B" 
      by blast

subsection ‹Trivial sets›

text ‹A trivial set (i.e. singleton or empty), as in Mizar›
definition trivial where "trivial x = (x  {the_elem x})"

text ‹The empty set is trivial.›
lemma trivial_empty: "trivial {}" 
      unfolding trivial_def by (rule empty_subsetI)

text ‹A singleton set is trivial.›
lemma trivial_singleton: "trivial {x}" 
      unfolding trivial_def by simp

text ‹If a trivial set has a singleton subset, the latter is unique.›
lemma singleton_sub_trivial_uniq:
      fixes   x X
      assumes "{x}  X" and "trivial X"
      shows   "x = the_elem X"
(* CL: The following takes 16 ms in Isabelle2013-1-RC1:
   by (metis assms(1) assms(2) insert_not_empty insert_subset subset_empty subset_insert trivial_def trivial_imp_no_distinct) *)
      using assms unfolding trivial_def by fast

text ‹Any subset of a trivial set is trivial.›

lemma trivial_subset: fixes X Y assumes "trivial Y" assumes "X  Y" 
                      shows "trivial X"
(* CL: The following takes 36 ms in Isabelle2013-1-RC1:
   by (metis assms(1) assms(2) equals0D no_distinct_imp_trivial subsetI subset_antisym subset_singletonD trivial_cases) *)
        using assms unfolding trivial_def 
        by (metis (full_types) subset_empty subset_insertI2 subset_singletonD)

text ‹There are no two different elements in a trivial set.›

lemma trivial_imp_no_distinct:
  assumes triv: "trivial X" and x: "x  X" and y: "y  X"
  shows   "x = y"
(* CL: The following takes 17 ms in Isabelle2013-1-RC1: *)
  using assms by (metis empty_subsetI insert_subset singleton_sub_trivial_uniq) 

subsection ‹The image of a set under a function›

text ‹an equivalent notation for the image of a set, using set comprehension›
lemma image_Collect_mem: "{ f x | x . x  S } = f ` S" 
      by auto

subsection ‹Big Union›

text ‹An element is in the union of a family of sets if it is in one of the family's member sets.›

lemma Union_member: "( S  F . x  S)  x   F" 
      by blast

subsection ‹Miscellaneous›

lemma trivial_subset_non_empty: assumes "trivial t" "t  X  {}" 
            shows   "t  X" 
      using trivial_def assms in_mono by fast

lemma trivial_implies_finite: assumes "trivial X" 
            shows   "finite X" 
      using assms by (metis finite.simps subset_singletonD trivial_def)
(* finite.simps trivial_cases by metis *)

lemma lm01: assumes "trivial (A × B)" 
              shows   "(finite (A×B) & card A * (card B)  1)" 
      using trivial_def assms One_nat_def card_cartesian_product card.empty card_insert_disjoint
            empty_iff finite.emptyI le0 trivial_implies_finite order_refl subset_singletonD by (metis(no_types))

lemma lm02: assumes "finite X" 
            shows   "trivial X=(card X  1)" 
      using assms One_nat_def card.empty card_insert_if card_mono card_seteq empty_iff 
            empty_subsetI finite.cases finite.emptyI finite_insert insert_mono 
            trivial_def trivial_singleton
      by (metis(no_types))

lemma lm03: shows "trivial {x}" 
      by (metis order_refl the_elem_eq trivial_def)

lemma lm04: assumes "trivial X" "{x}  X" 
            shows   "{x} = X" 
      using singleton_sub_trivial_uniq assms by (metis subset_antisym trivial_def)

lemma lm05: assumes "¬ trivial X" "trivial T" 
            shows   "X - T    {}"
      using assms by (metis Diff_iff empty_iff subsetI trivial_subset)

lemma lm06: assumes "(finite (A × B)  &  card A * (card B)  1)" 
              shows   "trivial (A × B)" 
      unfolding trivial_def using trivial_def assms by (metis card_cartesian_product lm02)

lemma lm07: "trivial (A × B) = (finite (A × B) & card A * (card B)  1)" 
      using lm01 lm06 by blast

lemma trivial_empty_or_singleton: "trivial X = (X = {}  X = {the_elem X})" 
      by (metis subset_singletonD trivial_def trivial_empty trivial_singleton)

lemma trivial_cartesian: assumes "trivial X" "trivial Y" 
            shows   "trivial (X × Y)"
      using assms lm07 One_nat_def Sigma_empty1 Sigma_empty2 card.empty card_insert_if
            finite_SigmaI trivial_implies_finite nat_1_eq_mult_iff order_refl subset_singletonD trivial_def trivial_empty
      by (metis (full_types))

lemma trivial_same: "trivial X = (x1  X. x2  X. x1 = x2)" 
      using trivial_def trivial_imp_no_distinct ex_in_conv insertCI subsetI subset_singletonD
      by (metis (no_types, opaque_lifting))

lemma lm08: assumes "(Pow X  {{},X})" 
              shows  "trivial X" 
      unfolding trivial_same using assms by auto

lemma lm09: assumes "trivial X" 
              shows "(Pow X  {{},X})" 
      using assms trivial_same by fast

lemma lm10: "trivial X = (Pow X  {{},X})" 
      using lm08 lm09 by metis

lemma lm11: "({x} × UNIV)  P = {x} × (P `` {x})" 
      by fast

lemma lm12: "(x,y)  P = (y  P``{x})" 
      by simp

lemma lm13: assumes "inj_on f A" "inj_on f B" 
             shows   "inj_on f (A  B)  =  (f`(A-B)  (f`(B-A)) = {})"
      using assms inj_on_Un by (metis)

lemma injection_union: assumes "inj_on f A" "inj_on f B" "(f`A)  (f`B) = {}" 
              shows "inj_on f (A  B)" 
      using assms lm13 by fast

lemma lm14: "(Pow X = {X}) = (X={})" 
      by auto