%------------------------------------------------------------------------------
% Subset Algebra Definition File
%
% Author: David Lester, Manchester University, NIA, Université Perpignan
%
% Version 1.0 8/7/04 Initial Version
%------------------------------------------------------------------------------
subset_algebra_def[T:TYPE]: THEORY
BEGIN
IMPORTING sets_aux@countable_props,
structures@fun_preds_partial[nat,set[T],reals.<=,subset?[T]],
sets_aux@indexed_sets_aux[nat,T], % Proof only
sets_aux@countable_indexed_sets[T], % Proof only
sets_aux@nat_indexed_sets[T], % Proof only
sets_aux@countable_image % Proof only
n,i: VAR nat
a,b: VAR set[T]
S,X,Y: VAR setofsets[T]
NX: VAR (nonempty?[set[T]])
E: VAR sequence[set[T]]
subset_algebra_empty?(S): bool = member(emptyset[T],S)
subset_algebra_complement?(S): bool = FORALL (x:(S)): member(complement(x),S)
subset_algebra_union?(S): bool = FORALL (x,y:(S)): member(union(x,y),S)
subset_algebra?(S):bool = subset_algebra_empty?(S) AND
subset_algebra_complement?(S) AND
subset_algebra_union?(S)
sigma_algebra_union?(S): bool = FORALL X: is_countable[set[T]](X) AND
(FORALL (x:(X)): member(x,S)) =>
member(Union(X),S)
sigma_algebra?(S):bool = subset_algebra_empty?(S) AND
subset_algebra_complement?(S) AND
sigma_algebra_union?(S)
sigma_union_implies_subset_union: LEMMA
sigma_algebra_union?(S) => subset_algebra_union?(S)
sigma_algebra_implies_subset_algebra: LEMMA
sigma_algebra?(S) => subset_algebra?(S)
trivial_subset_algebra:(subset_algebra?)
= union(singleton(emptyset[T]),singleton(fullset[T]))
subset_algebra: TYPE+ = (subset_algebra?) CONTAINING trivial_subset_algebra
sigma_algebra: TYPE+ = (sigma_algebra?) CONTAINING trivial_subset_algebra
A: VAR sigma_algebra
I: VAR set[sigma_algebra]
sigma_algebra_is_subset_algebra:
JUDGEMENT sigma_algebra SUBTYPE_OF subset_algebra
powerset_is_sigma_algebra: LEMMA sigma_algebra?(powerset(fullset[T]))
generated_sigma_algebra(X):sigma_algebra
= Intersection({Y | sigma_algebra?(Y) AND subset?(X,Y)})
generated_sigma_algebra_subset1: LEMMA
subset?(X,generated_sigma_algebra(X))
generated_sigma_algebra_subset2: LEMMA
subset?(X,Y) AND sigma_algebra?(Y) =>
subset?(generated_sigma_algebra(X),Y)
generated_sigma_algebra_idempotent: LEMMA generated_sigma_algebra(A) = A
intersection_sigma_algebra: LEMMA FORALL (A,B:sigma_algebra):
sigma_algebra?(intersection(A,B))
sigma(I):sigma_algebra = generated_sigma_algebra(Union(I))
sigma_member: LEMMA member(A,I) => subset?(A,sigma(I))
B: VAR subset_algebra
J: VAR set[subset_algebra]
powerset_is_subset_algebra: LEMMA subset_algebra?(powerset(fullset[T]))
generated_subset_algebra(X):subset_algebra
= Intersection({Y | subset_algebra?(Y) AND subset?(X,Y)})
generated_subset_algebra_subset1: LEMMA
subset?(X,generated_subset_algebra(X))
generated_subset_algebra_subset2: LEMMA
subset?(X,Y) AND subset_algebra?(Y) =>
subset?(generated_subset_algebra(X),Y)
generated_subset_algebra_idempotent: LEMMA generated_subset_algebra(B) = B
intersection_subset_algebra: LEMMA FORALL (A,B:subset_algebra):
subset_algebra?(intersection(A,B))
subset(J):subset_algebra = generated_subset_algebra(Union(J))
subset_member: LEMMA member(B,J) => subset?(B,subset(J))
finite_disjoint_union?(X)(a):bool
= EXISTS E,n: disjoint?(E) AND a = IUnion(E) AND
(FORALL i: (i < n => member(E(i),X)) AND
(i >= n => empty?(E(i))))
finite_disjoint_union_of?(X)(a)(E,n):bool
= disjoint?(E) AND a = IUnion(E) AND
(FORALL i: (i < n => member(E(i),X)) AND (i >= n => empty?(E(i))))
card(X:setofsets[T],a:(finite_disjoint_union?(X))):nat
= min({n:nat | EXISTS E: finite_disjoint_union_of?(X)(a)(E,n)})
finite_disjoint_unions(X):setofsets[T] = fullset[(finite_disjoint_union?(X))]
disjoint_algebra_construction: LEMMA % SKB 4.6.1
(FORALL (a,b:(NX)): member(intersection(a,b),NX)) AND
(FORALL (a:(NX)): finite_disjoint_union?(NX)(complement(a))) =>
generated_subset_algebra(NX) = finite_disjoint_unions(NX)
monotone?(X):bool
= FORALL E: (FORALL n: member(E(n),X)) => % SKB 4.6.4
((increasing?(E) => member(IUnion(E),X)) AND
(decreasing?(E) => member(IIntersection(E),X)))
monotone_class: TYPE+ = (monotone?) CONTAINING trivial_subset_algebra
powerset_is_monotone: LEMMA monotone?(powerset(fullset[T]))
sigma_algebra_is_monotone_class:
JUDGEMENT sigma_algebra SUBTYPE_OF monotone_class
monotone_algebra_is_sigma: LEMMA subset_algebra?(X) AND monotone?(X) =>
sigma_algebra?(X)
C: VAR monotone_class
K: VAR set[monotone_class]
monotone_class_Intersection: LEMMA monotone?(Intersection(K))
monotone_class: THEOREM % SKB 4.6.6
subset?(B,C) => subset?(generated_sigma_algebra(B),C)
END subset_algebra_def
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