diff --git a/build.gradle.kts b/build.gradle.kts
index fbb7fb5716..d15c6050b4 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -62,6 +62,8 @@ allprojects {
             "java.util.BitSet.get",  // moved
             "kotlin.collections.getValue", // moved
             "kotlin.collections.randomOrNull",
+            "kotlin.collections.Collection.isEmpty",
+            "kotlin.collections.subtract"
         )
         wellKnownPureClasses = setOf<String>(
         )
diff --git a/core/src/com/unciv/logic/city/CityConstructions.kt b/core/src/com/unciv/logic/city/CityConstructions.kt
index 8d6f633fa7..326fe07b6a 100644
--- a/core/src/com/unciv/logic/city/CityConstructions.kt
+++ b/core/src/com/unciv/logic/city/CityConstructions.kt
@@ -266,6 +266,7 @@ class CityConstructions : IsPartOfGameInfoSerialization {
             else 0
     }
 
+    @Readonly
     fun getRemainingWork(constructionName: String, useStoredProduction: Boolean = true): Int {
         val constr = getConstruction(constructionName)
         return when {
diff --git a/core/src/com/unciv/logic/civilization/Civilization.kt b/core/src/com/unciv/logic/civilization/Civilization.kt
index 0f1866cd63..e06f8ba55c 100644
--- a/core/src/com/unciv/logic/civilization/Civilization.kt
+++ b/core/src/com/unciv/logic/civilization/Civilization.kt
@@ -380,11 +380,11 @@ class Civilization : IsPartOfGameInfoSerialization {
     var cityStatePersonality: CityStatePersonality = CityStatePersonality.Neutral
     var cityStateResource: String? = null
     var cityStateUniqueUnit: String? = null // Unique unit for militaristic city state. Might still be null if there are no appropriate units
-
-    fun hasMetCivTerritory(otherCiv: Civilization): Boolean =
+    
+    @Readonly fun hasMetCivTerritory(otherCiv: Civilization): Boolean =
             otherCiv.getCivTerritory().any { gameInfo.tileMap[it].isExplored(this) }
     @Readonly fun getCompletedPolicyBranchesCount(): Int = policies.adoptedPolicies.count { Policy.isBranchCompleteByName(it) }
-    private fun getCivTerritory() = cities.asSequence().flatMap { it.tiles.asSequence() }
+    @Readonly private fun getCivTerritory() = cities.asSequence().flatMap { it.tiles.asSequence() }
 
     @Readonly
     fun getPreferredVictoryTypes(): List<String> {
@@ -463,7 +463,7 @@ class Civilization : IsPartOfGameInfoSerialization {
         return newResourceSupplyList
     }
 
-    fun isCapitalConnectedToCity(city: City): Boolean = cache.citiesConnectedToCapitalToMediums.keys.contains(city)
+    @Readonly fun isCapitalConnectedToCity(city: City): Boolean = cache.citiesConnectedToCapitalToMediums.keys.contains(city)
 
 
     /**
diff --git a/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt b/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt
index b37a1fb077..0aaae453c8 100644
--- a/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt
+++ b/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt
@@ -187,6 +187,7 @@ class CityStateFunctions(val civInfo: Civilization) {
         )
     }
 
+    @Readonly
     fun influenceGainedByGift(donorCiv: Civilization, giftAmount: Int): Int {
         // https://github.com/Gedemon/Civ5-DLL/blob/aa29e80751f541ae04858b6d2a2c7dcca454201e/CvGameCoreDLL_Expansion1/CvMinorCivAI.cpp
         // line 8681 and below
diff --git a/core/src/com/unciv/logic/civilization/managers/GreatPersonManager.kt b/core/src/com/unciv/logic/civilization/managers/GreatPersonManager.kt
index 548bec538f..2dfff4cd5c 100644
--- a/core/src/com/unciv/logic/civilization/managers/GreatPersonManager.kt
+++ b/core/src/com/unciv/logic/civilization/managers/GreatPersonManager.kt
@@ -7,6 +7,7 @@ import com.unciv.logic.civilization.NotificationCategory
 import com.unciv.models.Counter
 import com.unciv.models.ruleset.unique.UniqueType
 import com.unciv.ui.components.MayaCalendar
+import yairm210.purity.annotations.Readonly
 
 
 // todo: Great Admiral?
@@ -46,11 +47,12 @@ class GreatPersonManager : IsPartOfGameInfoSerialization {
         return toReturn
     }
 
+    @Readonly
     private fun getPoolKey(greatPerson: String) = civInfo.getEquivalentUnit(greatPerson)
         .getMatchingUniques(UniqueType.GPPointPool)
         // An empty string is used to indicate the Unique wasn't found
         .firstOrNull()?.params?.get(0) ?: ""
-
+    
     fun getPointsRequiredForGreatPerson(greatPerson: String): Int {
         val key = getPoolKey(greatPerson)
         if (pointsForNextGreatPersonCounter[key] == 0) {
@@ -102,12 +104,14 @@ class GreatPersonManager : IsPartOfGameInfoSerialization {
     }
 
     /** Get Great People specific to this manager's Civilization, already filtered by `isHiddenBySettings` */
+    @Readonly
     fun getGreatPeople() = civInfo.gameInfo.ruleset.units.values.asSequence()
         .filter { it.isGreatPerson }
         .map { civInfo.getEquivalentUnit(it.name) }
         .filterNot { it.isUnavailableBySettings(civInfo.gameInfo) }
         .toHashSet()
 
+    @Readonly
     fun getGreatPersonPointsForNextTurn(): Counter<String> {
         val greatPersonPoints = Counter<String>()
         for (city in civInfo.cities) greatPersonPoints.add(city.getGreatPersonPoints())
diff --git a/core/src/com/unciv/logic/civilization/managers/QuestManager.kt b/core/src/com/unciv/logic/civilization/managers/QuestManager.kt
index 5ce7898181..62e32b162f 100644
--- a/core/src/com/unciv/logic/civilization/managers/QuestManager.kt
+++ b/core/src/com/unciv/logic/civilization/managers/QuestManager.kt
@@ -33,6 +33,7 @@ import com.unciv.models.translations.getPlaceholderParameters
 import com.unciv.models.translations.tr
 import com.unciv.ui.components.extensions.toPercent
 import com.unciv.utils.randomWeighted
+import yairm210.purity.annotations.Readonly
 import kotlin.random.Random
 
 class QuestManager : IsPartOfGameInfoSerialization {
@@ -80,21 +81,24 @@ class QuestManager : IsPartOfGameInfoSerialization {
     private var unitsKilledFromCiv: HashMap<String, HashMap<String, Int>> = HashMap()
 
     /** Returns true if [civ] have active quests for [challenger] */
-    fun haveQuestsFor(challenger: Civilization): Boolean = getAssignedQuestsFor(challenger.civName).any()
+    @Readonly fun haveQuestsFor(challenger: Civilization): Boolean = getAssignedQuestsFor(challenger.civName).any()
 
     /** Access all assigned Quests for [civName] */
+    @Readonly
     fun getAssignedQuestsFor(civName: String) =
         assignedQuests.asSequence().filter { it.assignee == civName }
 
     /** Access all assigned Quests of "type" [questName] */
     // Note if we decide to cache an index of these (such as `assignedQuests.groupBy { it.questNameInstance }`), this accessor would simplify the transition
+    @Readonly
     private fun getAssignedQuestsOfName(questName: QuestName) =
         assignedQuests.asSequence().filter { it.questNameInstance == questName }
 
     /** Returns true if [civ] has asked anyone to conquer [target] */
-    fun wantsDead(target: String): Boolean = getAssignedQuestsOfName(QuestName.ConquerCityState).any { it.data1 == target }
+    @Readonly fun wantsDead(target: String): Boolean = getAssignedQuestsOfName(QuestName.ConquerCityState).any { it.data1 == target }
 
     /** Returns the influence multiplier for [donor] from a Investment quest that [civ] might have (assumes only one) */
+    @Readonly
     fun getInvestmentMultiplier(donor: String): Float {
         val investmentQuest = getAssignedQuestsOfName(QuestName.Invest).firstOrNull { it.assignee == donor }
             ?: return 1f
@@ -367,12 +371,14 @@ class QuestManager : IsPartOfGameInfoSerialization {
     }
 
     /** Returns true if [civ] can assign a quest to [challenger] */
+    @Readonly
     private fun canAssignAQuestTo(challenger: Civilization): Boolean {
         return !challenger.isDefeated() && challenger.isMajorCiv() &&
                 civ.knows(challenger) && !civ.isAtWarWith(challenger)
     }
 
     /** Returns true if the [quest] can be assigned to [challenger] */
+    @Readonly
     private fun isQuestValid(quest: Quest, challenger: Civilization): Boolean {
         if (!canAssignAQuestTo(challenger))
             return false
@@ -403,6 +409,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
         }
     }
 
+    @Readonly
     private fun isRouteQuestValid(challenger: Civilization): Boolean {
         if (challenger.cities.isEmpty()) return false
         if (challenger.isCapitalConnectedToCity(civ.getCapital()!!)) return false
@@ -414,6 +421,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
         }
     }
 
+    @Readonly
     private fun isDenounceCivQuestValid(challenger: Civilization, mostRecentBully: String?): Boolean {
         return mostRecentBully != null
             && challenger.knows(mostRecentBully)
@@ -424,6 +432,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
     }
 
     /** Returns true if the [assignedQuest] is successfully completed */
+    @Readonly
     private fun isComplete(assignedQuest: AssignedQuest): Boolean {
         val assignee = civ.gameInfo.getCivilization(assignedQuest.assignee)
         return when (assignedQuest.questNameInstance) {
@@ -441,6 +450,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
     }
 
     /** Returns true if the [assignedQuest] request cannot be fulfilled anymore */
+    @Readonly
     private fun isObsolete(assignedQuest: AssignedQuest): Boolean {
         val assignee = civ.gameInfo.getCivilization(assignedQuest.assignee)
         return when (assignedQuest.questNameInstance) {
@@ -489,6 +499,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
     }
 
     /** Returns the score for the [assignedQuest] */
+    @Readonly
     private fun getScoreForQuest(assignedQuest: AssignedQuest): Int {
         val assignee = civ.gameInfo.getCivilization(assignedQuest.assignee)
 
@@ -545,6 +556,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
      *  Tied leaders are separated by ", " - translators cannot influence this, sorry.
      *  @param inquiringAssignedQuest Determines ["type"][AssignedQuest.questNameInstance] to find all competitors in [assignedQuests] and [viewing civ][AssignedQuest.assignee].
      */
+    @Readonly
     fun getScoreStringForGlobalQuest(inquiringAssignedQuest: AssignedQuest): String {
         require(inquiringAssignedQuest.assigner == civ.civName)
         require(inquiringAssignedQuest.isGlobal())
@@ -654,7 +666,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
 
     /** Gets notified when [killed]'s military unit was killed by [killer], for war with major pseudo-quest */
     fun militaryUnitKilledBy(killer: Civilization, killed: Civilization) {
-        if (!warWithMajorActive(killed)) return
+        if (!isWarWithMajorActive(killed)) return
 
         // No credit if we're at war or haven't met
         if (!civ.knows(killer) || civ.isAtWarWith(killer))  return
@@ -705,14 +717,11 @@ class QuestManager : IsPartOfGameInfoSerialization {
         unitsKilledFromCiv.remove(attacker.civName)
     }
 
-    fun warWithMajorActive(target: Civilization): Boolean {
-        return unitsToKillForCiv.containsKey(target.civName)
-    }
+    @Readonly fun isWarWithMajorActive(target: Civilization): Boolean = unitsToKillForCiv.containsKey(target.civName)
 
-    fun unitsToKill(target: Civilization): Int {
-        return unitsToKillForCiv[target.civName] ?: 0
-    }
+    @Readonly fun unitsToKill(target: Civilization): Int = unitsToKillForCiv[target.civName] ?: 0
 
+    @Readonly
     fun unitsKilledSoFar(target: Civilization, viewingCiv: Civilization): Int {
         val killMap = unitsKilledFromCiv[target.civName] ?: return 0
         return killMap[viewingCiv.civName] ?: 0
@@ -734,6 +743,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
     /**
      * Returns the weight of the [questName], depends on city state trait and personality
      */
+    @Readonly
     private fun getQuestWeight(questName: String): Float {
         var weight = 1f
         val quest = ruleset.quests[questName] ?: return 0f
@@ -751,6 +761,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
      * Returns a random [Tile] containing a Barbarian encampment within 8 tiles of [civ]
      * to be destroyed
      */
+    @Readonly
     private fun getBarbarianEncampmentForQuest(): Tile? {
         val encampments = civ.getCapital()!!.getCenterTile().getTilesInDistance(8)
                 .filter { it.improvement == Constants.barbarianEncampment }.toList()
@@ -764,6 +775,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
      * by the [civ] and the [challenger], and must be viewable by the [challenger];
      * if none exists, it returns null.
      */
+    @Readonly
     private fun getResourceForQuest(challenger: Civilization): TileResource? {
         val ownedByCityStateResources = civ.detailedCivResources.map { it.resource }
         val ownedByMajorResources = challenger.detailedCivResources.map { it.resource }
@@ -781,8 +793,9 @@ class QuestManager : IsPartOfGameInfoSerialization {
         return notOwnedResources.randomOrNull()
     }
 
+    @Readonly
     private fun getWonderToBuildForQuest(challenger: Civilization): Building? {
-        fun isMoreThanAQuarterDone(city: City, buildingName: String) =
+        @Readonly fun isMoreThanAQuarterDone(city: City, buildingName: String) =
             city.cityConstructions.getWorkDone(buildingName) * 3 > city.cityConstructions.getRemainingWork(buildingName)
         val wonders = ruleset.buildings.values
                 .filter { building ->
@@ -803,6 +816,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
     /**
      * Returns a random Natural Wonder not yet discovered by [challenger].
      */
+    @Readonly
     private fun getNaturalWonderToFindForQuest(challenger: Civilization): String? {
         val naturalWondersToFind = civ.gameInfo.tileMap.naturalWonders.subtract(challenger.naturalWonders)
 
@@ -812,6 +826,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
     /**
      * Returns a Great Person [BaseUnit] that is not owned by both the [challenger] and the [civ]
      */
+    @Readonly
     private fun getGreatPersonForQuest(challenger: Civilization): BaseUnit? {
         val ruleset = ruleset // omit if the accessor should be converted to a transient field
 
@@ -835,6 +850,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
      * Returns a random [Civilization] (major) that [challenger] has met, but whose territory he
      * cannot see; if none exists, it returns null.
      */
+    @Readonly
     private fun getCivilizationToFindForQuest(challenger: Civilization): Civilization? {
         val civilizationsToFind = challenger.getKnownCivs()
             .filter { it.isAlive() && it.isMajorCiv() && !challenger.hasMetCivTerritory(it) }
@@ -846,6 +862,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
     /**
      * Returns a city-state [Civilization] that [civ] wants to target for hostile quests
      */
+    @Readonly
     private fun getCityStateTarget(challenger: Civilization): Civilization? {
         val closestProximity = civ.gameInfo.getAliveCityStates()
             .mapNotNull { civ.proximity[it.civName] }.filter { it != Proximity.None }.minByOrNull { it.ordinal }
@@ -861,6 +878,7 @@ class QuestManager : IsPartOfGameInfoSerialization {
 
     /** Returns a [Civilization] of the civ that most recently bullied [civ].
      *  Note: forgets after 20 turns has passed! */
+    @Readonly
     private fun getMostRecentBully(): String? {
         val bullies = civ.diplomacy.values.filter { it.hasFlag(DiplomacyFlags.Bullied) }
         return bullies.maxByOrNull { it.getFlag(DiplomacyFlags.Bullied) }?.otherCivName
@@ -892,17 +910,17 @@ class AssignedQuest(
         questObject = quest ?: gameInfo.ruleset.quests[questName]!!
     }
 
-    fun isIndividual(): Boolean = !isGlobal()
-    fun isGlobal(): Boolean = questObject.isGlobal()
+    @Readonly fun isIndividual(): Boolean = !isGlobal()
+    @Readonly fun isGlobal(): Boolean = questObject.isGlobal()
     @Suppress("MemberVisibilityCanBePrivate")
-    fun doesExpire(): Boolean = questObject.duration > 0
-    fun isExpired(): Boolean = doesExpire() && getRemainingTurns() == 0
+    @Readonly fun doesExpire(): Boolean = questObject.duration > 0
+    @Readonly fun isExpired(): Boolean = doesExpire() && getRemainingTurns() == 0
     @Suppress("MemberVisibilityCanBePrivate")
-    fun getDuration(): Int = (gameInfo.speed.modifier * questObject.duration).toInt()
-    fun getRemainingTurns(): Int = (assignedOnTurn + getDuration() - gameInfo.turns).coerceAtLeast(0)
-    fun getInfluence() = questObject.influence
+    @Readonly fun getDuration(): Int = (gameInfo.speed.modifier * questObject.duration).toInt()
+    @Readonly fun getRemainingTurns(): Int = (assignedOnTurn + getDuration() - gameInfo.turns).coerceAtLeast(0)
+    @Readonly fun getInfluence() = questObject.influence
 
-    fun getDescription(): String = questObject.description.fillPlaceholders(data1)
+    @Readonly fun getDescription(): String = questObject.description.fillPlaceholders(data1)
 
     fun onClickAction() {
         when (questNameInstance) {
diff --git a/core/src/com/unciv/models/ruleset/Quest.kt b/core/src/com/unciv/models/ruleset/Quest.kt
index ab37107a6b..50405964f5 100644
--- a/core/src/com/unciv/models/ruleset/Quest.kt
+++ b/core/src/com/unciv/models/ruleset/Quest.kt
@@ -2,6 +2,7 @@ package com.unciv.models.ruleset
 
 import com.unciv.logic.civilization.Civilization
 import com.unciv.models.stats.INamed
+import yairm210.purity.annotations.Readonly
 
 enum class QuestName(val value: String) {
     Route("Route"),
@@ -24,7 +25,7 @@ enum class QuestName(val value: String) {
     None("")
     ;
     companion object {
-        fun find(value: String) = values().firstOrNull { it.value == value } ?: None
+        fun find(value: String) = entries.firstOrNull { it.value == value } ?: None
     }
 }
 
@@ -67,6 +68,6 @@ class Quest : INamed {
     var weightForCityStateType = HashMap<String, Float>()
 
     /** Checks if `this` is a Global quest */
-    fun isGlobal(): Boolean = type == QuestType.Global
-    fun isIndividual(): Boolean = !isGlobal()
+    @Readonly fun isGlobal(): Boolean = type == QuestType.Global
+    @Readonly fun isIndividual(): Boolean = !isGlobal()
 }
diff --git a/core/src/com/unciv/models/ruleset/unit/BaseUnit.kt b/core/src/com/unciv/models/ruleset/unit/BaseUnit.kt
index 7a47f6bb53..585791718e 100644
--- a/core/src/com/unciv/models/ruleset/unit/BaseUnit.kt
+++ b/core/src/com/unciv/models/ruleset/unit/BaseUnit.kt
@@ -371,6 +371,7 @@ class BaseUnit : RulesetObject(), INonPerpetualConstruction {
 
     // This returns the name of the unit this tech upgrades this unit to,
     // or null if there is no automatic upgrade at that tech.
+    @Readonly
     fun automaticallyUpgradedInProductionToUnitByTech(techName: String): String? {
         for (obsoleteTech: String in techsAtWhichAutoUpgradeInProduction())
             if (obsoleteTech == techName)
@@ -405,6 +406,7 @@ class BaseUnit : RulesetObject(), INonPerpetualConstruction {
         }
     }
 
+    @Readonly
     fun getReplacedUnit(ruleset: Ruleset): BaseUnit {
         return if (replaces == null) this
         else ruleset.units[replaces!!]!!
diff --git a/core/src/com/unciv/models/ruleset/validation/Suppression.kt b/core/src/com/unciv/models/ruleset/validation/Suppression.kt
index 2eb27b15e7..67ca054424 100644
--- a/core/src/com/unciv/models/ruleset/validation/Suppression.kt
+++ b/core/src/com/unciv/models/ruleset/validation/Suppression.kt
@@ -11,6 +11,7 @@ import com.unciv.models.ruleset.unique.UniqueParameterType
 import com.unciv.models.ruleset.unique.UniqueType
 import com.unciv.models.translations.fillPlaceholders
 import yairm210.purity.annotations.Pure
+import yairm210.purity.annotations.Readonly
 
 /**
  *  All public methods dealing with how Mod authors can suppress RulesetValidator output.
@@ -65,6 +66,7 @@ object Suppression {
         else -> true
     }
 
+    @Pure
     private fun matchesFilter(error: RulesetError, filter: String): Boolean {
         if (error.text == filter) return true
         if (!filter.endsWith('*') || !filter.startsWith('*')) return false
@@ -72,6 +74,7 @@ object Suppression {
     }
 
     /** Determine if [error] matches any suppression Unique in [ModOptions] or the [sourceObject], or any suppression modifier in [sourceUnique] */
+    @Readonly
     internal fun isErrorSuppressed(
         globalSuppressionFilters: Collection<String>,
         sourceObject: IHasUniques?,
@@ -81,6 +84,7 @@ object Suppression {
         if (error.errorSeverityToReport >= RulesetErrorSeverity.Error) return false
         if (sourceObject == null && globalSuppressionFilters.isEmpty()) return false
 
+        @Readonly
         fun getWildcardFilter(unique: Unique) = unique.params[0].let {
             if (it.startsWith('*')) it else "*$it*"
         }
diff --git a/core/src/com/unciv/ui/screens/diplomacyscreen/CityStateDiplomacyTable.kt b/core/src/com/unciv/ui/screens/diplomacyscreen/CityStateDiplomacyTable.kt
index 2b8a6196f3..ca04e9fb9c 100644
--- a/core/src/com/unciv/ui/screens/diplomacyscreen/CityStateDiplomacyTable.kt
+++ b/core/src/com/unciv/ui/screens/diplomacyscreen/CityStateDiplomacyTable.kt
@@ -86,7 +86,7 @@ class CityStateDiplomacyTable(private val diplomacyScreen: DiplomacyScreen) {
             diplomacyTable.add(getQuestTable(assignedQuest)).row()
         }
 
-        for (target in otherCiv.getKnownCivs().filter { otherCiv.questManager.warWithMajorActive(it) && viewingCiv != it }) {
+        for (target in otherCiv.getKnownCivs().filter { otherCiv.questManager.isWarWithMajorActive(it) && viewingCiv != it }) {
             diplomacyTable.addSeparator()
             diplomacyTable.add(getWarWithMajorTable(target, otherCiv)).row()
         }