什麽是形式集合Formal Sets/PowerFormalSet？

lilianjie

哪位能给理解下：

Formal Sets
# {/ n9 e8 i7 E% h) ?6 QA formal set consists of the subset of elements of some carrier set (structure) on which a certain predicate assumes the value `true'.

The only set-theoretic operations that can be performed on formal sets are union, intersection, difference and symmetric difference, and element membership testing.



S := { 1 .. 5};
$ Y+ ?/ j; w8 M0 [& g0 I& _> P := PowerSet(S);
) }2 r: f! Z2 Y6 D  x3 o" jP;
PFS:=PowerFormalSet(S);
PFS;
F := { 2, 4 };
: G. m: Z9 L2 y% @' j% nFF := { 2/3, 4 };
. v" u( |7 p$ M" R+ x
. ]' `& W) X0 M% ?% W1 _+ ^% A2 f3 } F in P;
1 K, e* B" Y5 {/ ~: i% z8 q4 ^+ yFF in P;
) T: _- E9 j8 o- a3 z  u/ s F in PFS;
FF in PFS;
* X; P' M( |" q$ LSet of subsets of { 1 .. 5 }
Set of formal subsets of { 1 .. 5 }
true
false

>>  F in PFS;
      ^
Runtime error in 'in': Bad argument types


, G* D& M# m' @8 i7 A: {>> FF in PFS;
      ^
3 @( k7 L8 @4 m. O1 ~* lRuntime error in 'in': Bad argument types