哪位能给理解下: 8 A$ e. o4 L+ c$ `2 e 6 \, \7 p+ ?+ dFormal Sets" b! o& b- x$ [
A formal set consists of the subset of elements of some carrier set (structure) on which a certain predicate assumes the value `true'. : k3 d0 \7 b# f4 c5 g. ^/ L% j! i 6 O8 x! [1 o6 PThe only set-theoretic operations that can be performed on formal sets are union, intersection, difference and symmetric difference, and element membership testing. ' ^0 P: a) k- Z# G! m" F% l7 k: a: F% Q' @( W% |9 `) S
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S := { 1 .. 5}; ' i+ m! `' g( i" m# o {> P := PowerSet(S); 8 e4 [& x2 m7 n( MP;5 f) ~* Y) O, x2 e& p% W5 k
PFS:=PowerFormalSet(S);8 v% I3 g& }: ]* D2 w
PFS; 2 ?" O( q( J$ ~( B1 g" I- Q* R8 e5 wF := { 2, 4 }; 9 s# J( l& K) d% Z- X x# u. M( `FF := { 2/3, 4 }; t& M; k; U- r1 E
5 m! p7 x4 x" w4 } F in P; : X5 G+ h1 O0 n# X. O* f- |FF in P; / [9 h4 @- X( I+ b" o F in PFS;7 G6 A( H3 a5 x; s" _" F/ f* j3 r/ P
FF in PFS; 1 v( ]( A0 i0 Q* `; L' i/ ^( B# QSet of subsets of { 1 .. 5 } 7 |- l7 b+ o. M8 O% ^Set of formal subsets of { 1 .. 5 } " g; b2 ^+ B- o0 Q; Z, }true - ]& p9 H1 E% T$ @false m8 ?/ }% E F. X
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>> F in PFS;2 \- J& [( X0 a3 v9 {8 c
^ ; E& J; _ @- v" wRuntime error in 'in': Bad argument types4 @0 p4 z/ X# y' E
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>> FF in PFS; 8 }. _" @* S O3 O# j% t% k$ y ^- S; q/ E* _0 D" s* _# |) ^ I' r
Runtime error in 'in': Bad argument types