什麽是形式集合Formal Sets/PowerFormalSet？

lilianjie

哪位能给理解下：
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0 Z1 I0 m; o2 ?$ GFormal Sets
A formal set consists of the subset of elements of some carrier set (structure) on which a certain predicate assumes the value `true'.

( s4 \5 ?. x3 P; G! A9 dThe only set-theoretic operations that can be performed on formal sets are union, intersection, difference and symmetric difference, and element membership testing.
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0 E* ^/ C" S! l$ T: ^. m# hS := { 1 .. 5};
0 q' Y* ?: f: h: I4 D2 h6 M> P := PowerSet(S);
P;
+ u/ k; R! f" DPFS:=PowerFormalSet(S);
- {4 i8 I7 T' S# _  W7 m3 i5 I: S9 vPFS;
F := { 2, 4 };
/ l; d. z% I- m$ G3 B+ B5 P/ I. w9 OFF := { 2/3, 4 };

F in P;
FF in P;
5 A# l/ w0 E# G: C3 p  Z, k/ r F in PFS;
FF in PFS;
Set of subsets of { 1 .. 5 }
Set of formal subsets of { 1 .. 5 }
( q' f1 @- {2 M4 m% M- gtrue
! K) F8 O: D' f1 D! Nfalse
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! a. L6 N/ n$ L& [" L& T>>  F in PFS;
* G4 T0 u/ g8 }  ]1 J% V      ^
Runtime error in 'in': Bad argument types
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' P' e1 I; z. V' ?' T! [. X8 U- x>> FF in PFS;
      ^
; Y/ y) T% ]/ wRuntime error in 'in': Bad argument types