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Refine problem 4
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typst/hw4.typ

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@@ -170,33 +170,31 @@ Minik replies: "Excellent. Then we shall certainly sell you either the Elephandr
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How many companions were actually purchased?
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== Problem 4: Voting Protocol
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== Problem 4: The Consensus Engine
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Ijon Tichy mediates a constitutional crisis on the *Galactic Council*.
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Five member worlds --- Alderan, Betelgeuse, Centauri, Deneb, and Eridani --- must adopt a new voting protocol.
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Their automated legal verification system uses symbolic constraint solving: all political rules must be expressed in CNF (conjunctive normal form) so the system can check whether any legal configuration is possible.
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The Galactic Council's legal automation system requires all voting rules in Conjunctive Normal Form --- "to reason about politics," the engineers say, "one must encode it."
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Tichy must formalize five worlds' fractious voting protocol, lest deadlock becomes constitutional.
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Let $A$, $B$, $C$, $D$, $E$ denote "member world voted yes."
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+ *Majority support:*
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The Council's charter requires majority support: encode "at least 3 of 5 voted yes" in CNF.
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Count the resulting clauses.
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+ *Supermajority:*
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Democracy requires quorum: encode _"at least 3 worlds vote yes"_ in CNF.
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+ *Opposition safeguard:*
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To prevent tyranny by dissenters, the Council imposes a stricter constraint: no _single world_ may block a proposal.
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Formalize and encode "at most 1 world votes no" in CNF.
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Count the resulting clauses.
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+ *Tyranny safeguard:*
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Ancient law forbids unanimous approval.
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Encode _"at most 4 worlds vote yes"_ in CNF.
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+ *Alderan's privilege:*
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Alderan (the elder civilization) enjoys special status: a proposal passes if either (at least 3 worlds approve) OR (Alderan approves alone, with or without support).
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Formalize this rule and convert to CNF.
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The elder Alderan civilization bypasses the quorum: a proposal passes if either _at least 3 worlds approve_ *or* _Alderan approves (regardless of others)_.
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Formalize this in CNF.
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+ *Efficient cardinality encoding:*
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The verification system struggles with the growing number of clauses from the encodings above.
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Generalize: design a compact encoding for "at least $k$ of $n$ variables are true, and at most $m$ are true" (where $k <= m$) using auxiliary variables.
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+ *Efficient encoding:*
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Naive cardinality constraints explode into clauses exponentially --- impractical for real councils.
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Design a compact CNF encoding for the general constraint _"at least $k$ and at most $m$ of $n$ variables are true"_ (where $k <= m$) using _auxiliary variables_.
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For the Council case ($n=5, k=3, m=4$), count your encoding's clauses versus naive CNF.
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What architectural trade-off emerges between encoding size and solver efficiency?
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For the Council case ($n=5, k=3, m=4$), compare your encoding's clause count against the naive approach.
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What trade-off between encoding complexity and solver efficiency does this illustrate?
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