Hi José,in that case I'd suggest using a recursive definition such as the one below. In my original answer to Mariusz I tried to avoid using recursion, but this requires bounding the base set of sequences, which makes TLC balk when the sets are heterogeneous.I haven't tried writing a Java override of the operator definition.Regards,Stephan(***************************************************************************)(* Given a sequence s = <<S1, ..., Sn>> of sets, Cartesian(s) computes the *)(* n-ary Cartesian product of these sets, i.e. the set of all sequences *)(* whose i-th element belongs to the set Si. For example, *)(* Cartesian(<<{1,2}, {"a", "b"}, {{}}>>) = *)(* {<<1, "a", {}>>, <<1, "b", {}>>, <<2, "a", {}>>, <<2, "b", {}>>} *)(***************************************************************************)RECURSIVE Cartesian(_)Cartesian(s) ==IF s = << >> THEN { << >> }ELSE LET C == Cartesian(Tail(s))AllCons(seq) == { <<x>> \o seq : x \in Head(s) }IN UNION { AllCons(seq) : seq \in C }On 21 Oct 2020, at 02:42, JosEdu Solsona <josedu...@xxxxxxxxx> wrote:Hello,I'm wondering if it is possible to define a n-ary cartesian operator like the one proposed by Stephan:Cartesian(S) ==LET U == UNION Range(S)FSeq == [ (1 .. Len(S)) -> U ]IN {s \in FSeq : \A i \in 1 .. Len(s) : s[i] \in S[i]}except it also work with sequences of sets of possible different types.For example, TLC doesn't have any problem computing something like {1,2} \X {"A","B"}.But it will fail to evaluate Cartesian(<<{1,2},{"A","B"}>>) because it can't compare numbers with strings.Alternatively, can these "limitation" be circumvented if the operator is overridden with an appropriate Java method?Regards,JoséThanks Stephan and Markus!wtorek, 20 października 2020 o 18:57:00 UTC+2 Stephan Merz napisał(a):Thanks for the explanations. This operator (I renamed it to Shuffle for lack of a better name) could be defined as follows.Range(f) == {f[x] : x \in DOMAIN f}(***************************************************************************)(* If Sets is a set of (non-empty) sets then Choice(Sets) is the set of *)(* all choice functions over Sets, that is, functions that associate some *)(* with every set in Sets. *)(***************************************************************************)Choice(Sets) == { f \in [Sets -> UNION Sets] : \A S \in Sets : f[S] \in S }(***************************************************************************)(* Compute all sets that contain one element from each of the input sets: *)(* Shuffle({{1,2}, {3,4}, {5}}) = {{1,3,5}, {1,4,5}, {2,3,5}, {2,4,5}} *)(***************************************************************************)Shuffle(Sets) == { Range(f) : f \in Choice(Sets) }Regards,StephanOn 20 Oct 2020, at 14:09, Mariusz Ryndzionek <mrynd...@xxxxxxxxx> wrote:Okay, so I wasn't specific enough. I know that \X in TLA+ is not commutative and in fact not even associative.I wanted something that would give me:Cartesian({{1, 2}, {3, 4}, {5}}) = {{1, 3, 5}, {1, 4, 5}, {2, 3, 5}, {2, 4, 5}}Your last definition works in TLC. Thanks Stephan!Is the `Range` operator defined somewhere in official/builtin modules?Range(f) == { f[x] : x \in DOMAIN f }Regarding overriding in Java, is it recommended only for to performance reasons?wtorek, 20 października 2020 o 13:41:38 UTC+2 Stephan Merz napisał(a):Hello,your problem is not well specified because {S1, S2} = {S2, S1} but S1 \X S2 is different from S2 \X S1. Also, I don't understand your remark about the output: the cartesian product is a set, but its elements are sequences.Assuming that your operator takes a *sequence* of sets, i.e. Cartesian(<<S1, S2, ..., Sn>>), you can write the following in TLA+.Range(S) == { S[i] : i \in 1 .. Len(S) }Cartesian(S) ==LET U == UNION Range(S)IN {s \in Seq(U) : /\ Len(s) = Len(S)/\ \A i \in 1 .. Len(s) : s[i] \in S[i]}However, TLC will not be available to interpret this because of the quantification over the infinite set Set(U). The following should work in principle (I haven't actually tried):Cartesian(S) ==LET U == UNION Range(S)FSeq == [ (1 .. Len(s)) -> U ]IN {s \in FSeq : \A i \in 1 .. Len(s) : s[i] \in S[i]}However, you probably want to override this operator definition by a Java method.StephanOn 20 Oct 2020, at 13:27, Mariusz Ryndzionek <mrynd...@xxxxxxxxx> wrote:Hello,I need n-ary Cartesian product operator. Something that would do:Cartesian({S1, S2, .., Sn}) = S1 \X S2 \X .. SnThe output shouldn't necessarily be sequences. Sets will do.Is there already something like this in TLA+?Regards,Mariusz--
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