什麽是形式集合Formal Sets/PowerFormalSet？

lilianjie

哪位能给理解下：

- e4 G; w* u% @5 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'.

2 i/ y- ~; V; `9 r* M+ L& I) ]) YThe only set-theoretic operations that can be performed on formal sets are union, intersection, difference and symmetric difference, and element membership testing.


" @6 [5 b% r+ s& ^: r- L! r
1 C8 A9 Y3 E6 l" ?3 O1 qS := { 1 .. 5};
> P := PowerSet(S);
P;
4 @* u  }1 T, `4 n7 i( x. B3 ]7 \# GPFS:=PowerFormalSet(S);
PFS;
  y. R3 T' b; @; e  |4 ]F := { 2, 4 };
5 A1 C' w% E& `FF := { 2/3, 4 };
( e/ V9 j! u) c2 B# r( Q0 H
* y% w3 t, [# [8 L& w F in P;
( G& i1 o1 r1 T* uFF in P;
9 j. Y0 i. N& E8 x F in PFS;
FF in PFS;
& Z/ Q% b+ Y' ?Set of subsets of { 1 .. 5 }
& h2 ~" N9 O9 @* a0 A, a! |Set of formal subsets of { 1 .. 5 }
true
* ?/ @- o& p0 }+ W( X! U6 Q4 W' Lfalse
- N4 C1 [* w8 K8 ]' f
>>  F in PFS;
      ^
" z) X6 R3 `7 W/ K& W/ y5 wRuntime error in 'in': Bad argument types

* t9 ^3 t4 P: Y: t# h
>> FF in PFS;
      ^
Runtime error in 'in': Bad argument types