Tweaks
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8 changed files with 26 additions and 14 deletions
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@ -2330,6 +2330,15 @@
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@book{Bojanczyk18,
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author = {Miko{\l}aj Boja{\'{n}}czyk},
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title = {Slightly Infinite Sets},
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publisher = {Draft December 4, 2018},
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year = {2018},
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url = {https://www.mimuw.edu.pl/~bojan/upload/main-6.pdf}
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}
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@inproceedings{BojanczykKLT13,
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author = {Miko{\l}aj Boja{\'{n}}czyk and
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Bartek Klin and
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@ -11,7 +11,7 @@
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\midaligned{\framed[width=12cm,align=center,offset=2cm,frame=off]{Nominal Techniques \& Black Box Testing for Automata Learning}}
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\switchtobodyfont[12pt]
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\midaligned{Joshua Moerman}
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\midaligned{7 January 2019}
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\midaligned{8 January 2019}
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\stop
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\page[yes]
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@ -24,6 +24,7 @@
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\startbodymatter
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\setupheadertexts[{\sc {\getmarking[chapter]}}][\pagenumber][\pagenumber][{\sc Chapter {\getmarking[chapternumber]}}]
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\component content/introduction
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\startpart[title={Testing Techniques}, reference=part:testing]
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@ -41,6 +42,7 @@
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\startbackmatter
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\setupheadertexts[{\sc References}][\pagenumber][\pagenumber][{\sc References}]
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\switchtobodyfont[8pt]
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\title{References}
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\placelistofpublications
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@ -383,6 +383,7 @@ However, nominal sets are defined in a more elementary way.
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The nominal sets we will soon see are introduced by \citet[GabbayP02] to solve certain problems in name binding in abstract syntaxes.
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Although this is not really related to automata theory, it was picked up by \citet[BojanczykKL14],
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who provide an equivalence between register automata and nominal automata.
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(This equivalence is exposed in more detail in the book of \citet[Bojanczyk18].)
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Additionally, they generalise the work on nominal sets to other symmetries.
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The symmetries we encounter in this thesis are listed below, but other symmetries can be found in the literature.
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@ -64,9 +64,9 @@ This is relevant for name abstraction \citep[Pitts13], and has also been studied
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We apply these connections between nominal sets and renaming sets in the context of automata theory.
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Nominal automata are an elegant model for recognising languages over infinite alphabets.
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They are expressively equivalent to the more classical register automata,
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They are expressively equivalent to the more classical register automata (\citenp[Bojanczyk18], Theorem 6.5),
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and have appealing properties that register automata lack, such as unique minimal automata.
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However, moving from register automata to nominal automata can lead to an exponential blow-up in the number of states \citep[BojanczykKL14].
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However, moving from register automata to nominal automata can lead to an exponential blow-up in the number of states.
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\footnote{Here \quote{number of states} refers to the number of orbits in the state space.}
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As a motivating example, we consider a language modelling an $n$-bounded FIFO queue.
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@ -153,7 +153,7 @@ The powerset $\pow(X)$ of a nominal set is not nominal in general; the restricti
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If $M$ is a group, then the notion of support can be simplified by using inverses.
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To see this, first note that, given elements $g_1, g_2 \in M$, $g_1|_C = g_2|_C$ can equivalently be written as $g_1 g_2^{-1}|_C = \id|_C$.
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Second, the statement $x g_1 = x g_2$ can be expressed as $x g_1 g_2^{-1} = x$.
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Hence, $C$ is a support iff $g|_C = \id_C$ implies $gx = x$ for all $g$, which is the standard definition for nominal sets over a group \citep[BojanczykKL14, Pitts13].
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Hence, $C$ is a support iff $g|_C = \id_C$ implies $gx = x$ for all $g$, which is the standard definition for nominal sets over a group \citep[Pitts13].
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Surprisingly, \citet[GabbayH08] show a similar characterisation also holds for $\sb$-sets.
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Moreover, recall that every $\sb$-set is also a $\perm$-set; the associated notions of support coincide on nominal $\sb$-sets, as shown by the following result.
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In particular, this means that the forgetful functor restricts to $U \colon \sbnom \to \permnom$.
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@ -1118,12 +1118,12 @@ If two states $s, t$ are related by a bisimulation, then $s \sim t$.
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We use a slight generalisation of the bisimulation proof technique, callend \emph{bisimulation up-to}.
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This allows one to give a smaller set $R$ which extends to a bisimulation.
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A good introduction of these up-to techniques is given by \citet[BonchiP15] or the thesis of \citet[Rot17].
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In our case we use bisimulation \emph{up-to equivalence}.
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In our case we use bisimulation \emph{up-to ${\sim}$-union}.
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The following lemma can be found in the given references.
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\startdefinition
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Let $M$ be a Mealy machine.
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A relation $R \subseteq S \times S$ is called a \defn{bisimulation up-to equivalence} if for every $(s, t) \in R$ we have
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A relation $R \subseteq S \times S$ is called a \defn{bisimulation up-to ${\sim}$-union} if for every $(s, t) \in R$ we have
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\startitemize
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\item equal outputs: $\lambda(s, a) = \lambda(t, a)$ for all $a \in I$, and
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\item related successor states: $(\delta(s, a), \delta(t, a)) \in R$ \emph{or} $\delta(s, a) \sim \delta(t, a)$ for all $a \in I$.
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@ -1131,7 +1131,7 @@ A relation $R \subseteq S \times S$ is called a \defn{bisimulation up-to equival
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\stopdefinition
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\startlemma[reference=lem:bisim-upto]
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Any bisimulation up-to equivalence is contained in a bisimulation.
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Any bisimulation up-to ${\sim}$-union is contained in a bisimulation.
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\stoplemma
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We fix a specification $M$ which has a minimal representative with $n$ states and an implementation $M'$ with at most $n+k$ states.
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@ -1165,7 +1165,7 @@ Second, we show that the reached states are bisimilar.
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Define the relation $R = \{(\delta(s_0, p), \delta'(s_0', p)) \mid p \in P \cdot I^{\leq k}\}$.
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Note that for each $(s, i) \in R$ we have $s \sim_{W_s} i$.
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For each state $i \in M'$ there is a state $s \in M$ such that $(s, i) \in R$, since we reach all states in both machines by $P \cdot I^{\leq k}$.
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We will prove that this relation is in fact a bisimulation up-to equivalence.
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We will prove that this relation is in fact a bisimulation up-to ${\sim}$-union.
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For output, we note that $(s, i) \in R$ implies $\lambda(s, a) = \lambda'(i, a)$ for all $a$,
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since the machines agree on $P \cdot I^{\leq k+1}$.
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@ -1175,7 +1175,7 @@ We also know that we tested $i_2$ with the set $W'_t$.
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So we have:
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\startformula s_2 \sim_{W'_{s_2}} i_2 \sim_{W_t} t. \stopformula
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By the second assumption, we conclude that $s_2 \sim t$.
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So $s_2 \sim t$ and $(t, i) \in R$, which means that $R$ is a bisimulation up-to equivalence.
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So $s_2 \sim t$ and $(t, i) \in R$, which means that $R$ is a bisimulation up-to ${\sim}$-union.
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Moreover, $R$ contains the pair $(s_0, s'_0)$.
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By using \in{Lemma}[lem:bisim-upto] and \in{Lemma}[lem:bisim], we conclude that the initial $s_0$ and $s'_0$ are equivalent.
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\stopproof
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@ -1186,7 +1186,7 @@ This proof is very similar to the completeness proof by \citet[Chow78].
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In the first part we argue that all states are visited by using some sort of counting and reachability argument.
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Then in the second part we show the actual equivalence.
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To the best of the authors knowledge, this is first $m$-completeness proof which explicitly uses the concept of a bisimulation.
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Using a bisimulation allows us to slightly generalise and use bisimulation up-to equivalence, dropping the the often-assumed requirement that $M$ is minimal.
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Using a bisimulation allows us to slightly generalise and use bisimulation up-to ${\sim}$-union, dropping the the often-assumed requirement that $M$ is minimal.
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\startlemma
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Let $\Fam{W'}$ be a family of state identifiers for $M$.
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\setupexternalfigures[directory={images,../images}]
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% \definemode[afloop][yes]
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\definemode[afloop][yes]
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% \definemode[draft][yes]
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\environment bib
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@ -7,8 +7,8 @@
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\setuplist[part][style=bold, height=broad, starter={Part }, stopper={:}]
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% How numbers are shown
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\setuphead[part][placehead=yes, command=\MyPart]
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\setuphead[chapter][sectionsegments=chapter, command=\MyChapter]
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\setuphead[part][placehead=yes, command=\MyPart, header=empty]
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\setuphead[chapter][sectionsegments=chapter, command=\MyChapter, header=empty]
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\setuphead[section][sectionsegments=section]
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\setuphead[subsection][sectionsegments=section:subsection]
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