什麽是形式集合Formal Sets/PowerFormalSet？

lilianjie

哪位能给理解下：

Formal Sets
1 [* \3 R' T% V6 P0 E6 Y1 P  iA formal set consists of the subset of elements of some carrier set (structure) on which a certain predicate assumes the value `true'.

8 ]4 t* ~, O* e7 j! p. q+ M  tThe only set-theoretic operations that can be performed on formal sets are union, intersection, difference and symmetric difference, and element membership testing.

3 x) D" |+ i0 W# p
# o! B( f) E) p/ a8 r3 E! V
2 C6 `) P# ^' j' s0 l9 U1 OS := { 1 .. 5};
% @. w! s% {: I! _( V" z8 Q> P := PowerSet(S);
+ S! Z8 Q2 K0 d2 `6 x6 }P;
PFS:=PowerFormalSet(S);
PFS;
- Y/ Y# F/ I* B2 ?7 Z5 e, F; RF := { 2, 4 };
9 ?4 e1 z6 ]# DFF := { 2/3, 4 };
- w9 e0 }9 T7 b: _
F in P;
FF in P;
% Q( @" y8 j& P# y) H F in PFS;
7 S  B% [8 q% D, ^  S. PFF in PFS;
Set of subsets of { 1 .. 5 }
Set of formal subsets of { 1 .. 5 }
true
8 H3 x3 h9 g/ S  Y8 Nfalse
3 Z) w2 w/ Z0 i! o: }; n2 h
>>  F in PFS;
      ^
Runtime error in 'in': Bad argument types
/ B( {5 v* T6 J

) C. _3 X  h) A/ q& q>> FF in PFS;
- A0 Z0 L' Q2 |1 W6 ?7 B) I+ B      ^
Runtime error in 'in': Bad argument types