diff --git a/build.sbt b/build.sbt
index abbc298..6375a5e 100644
--- a/build.sbt
+++ b/build.sbt
@@ -8,6 +8,7 @@ lazy val commonSettings = Seq(
   organizationHomepage := Some(url("https://economicsl.github.io/")),
   libraryDependencies ++= Seq(
     "org.scalactic" %% "scalactic" % "3.0.5",
+    "org.typelevel" %% "cats-core" % "1.1.0",
     "com.typesafe.akka" %% "akka-actor" % "2.5.6",
     "org.economicsl" %% "esl-core" % "0.1.0-SNAPSHOT"
   ),
@@ -22,7 +23,8 @@ lazy val commonSettings = Seq(
     "-language:reflectiveCalls",  // needed in order to enable structural (or duck) typing
     "-Xlint",
     "-Ywarn-unused-import",
-    "-Ywarn-dead-code"
+    "-Ywarn-dead-code",
+    "-Ypartial-unification"
   )
 )
 
diff --git a/src/functional/scala/org/economicsl/matching/HouseListing.scala b/src/functional/scala/org/economicsl/matching/HouseListing.scala
index fd2f1c5..4c79af2 100644
--- a/src/functional/scala/org/economicsl/matching/HouseListing.scala
+++ b/src/functional/scala/org/economicsl/matching/HouseListing.scala
@@ -20,7 +20,7 @@ import java.util.UUID
 import org.economicsl.core.Price
 
 
-case class HouseListing(uuid: UUID, issuer: Long, price: Price, house: House)
+case class HouseListing(uuid: UUID, issuer: UUID, price: Price, house: House)
   extends Predicate[HousePurchaseOffer] with Preferences[HousePurchaseOffer] {
 
   /** Boolean function used to determine whether some `HousePurchaseOffer` is acceptable.
diff --git a/src/functional/scala/org/economicsl/matching/HouseMarketSpecification.scala b/src/functional/scala/org/economicsl/matching/HouseMarketSpecification.scala
index f5d418d..83c4b48 100644
--- a/src/functional/scala/org/economicsl/matching/HouseMarketSpecification.scala
+++ b/src/functional/scala/org/economicsl/matching/HouseMarketSpecification.scala
@@ -15,64 +15,64 @@ limitations under the License.
 */
 package org.economicsl.matching
 
+import cats.data.State
 import org.economicsl.core.Price
 import org.economicsl.matching.onetoone.DeferredAcceptanceAlgorithm
 import org.scalacheck.{Gen, Prop, Properties}
 
-import scala.collection.immutable.HashSet
-
 
 object HouseMarketSpecification extends Properties("housing-market") {
 
   // this generator should exist in esl-core!
-  val priceGen: Gen[Price] = {
+  def price: Gen[Price] = {
     for {
-      value <- Gen.choose(100000, 1000000)
+      value <- Gen.posNum[Long]
     } yield Price(value)
   }
 
-  val houseGen: Gen[House] = {
+  val house: Gen[House] = {
     for {
-      id <- Gen.uuid
-      quality <- Gen.choose(1, 100)
-    } yield House(id, quality)
+      uuid <- Gen.uuid
+      quality <- Gen.posNum[Int]
+    } yield House(uuid, quality)
   }
 
-  val houseListingGen: Gen[HouseListing] = {
+  val houseListing: Gen[HouseListing] = {
     for {
-      id <- Gen.uuid
-      issuer <-  Gen.posNum[Long]
-      price <-  priceGen
-      house <- houseGen
-    } yield HouseListing(id, issuer, price, house)
+      uuid <- Gen.uuid
+      issuer <-  Gen.uuid
+      price <-  price
+      house <- house
+    } yield HouseListing(uuid, issuer, price, house)
   }
 
-  val housePurchaseOfferGen: Gen[HousePurchaseOffer] = {
+  val housePurchaseOffer: Gen[HousePurchaseOffer] = {
     for {
-      id <- Gen.uuid
-      issuer <- Gen.posNum[Long]
-      price <- priceGen
-    } yield HousePurchaseOffer(id, issuer, price)
+      uuid <- Gen.uuid
+      issuer <- Gen.uuid
+      price <- price
+    } yield HousePurchaseOffer(uuid, issuer, price)
   }
 
-  val housePurchaseOffers: Gen[HashSet[HousePurchaseOffer]] = Gen.sized {
-    n => Gen.containerOfN[HashSet, HousePurchaseOffer](n, housePurchaseOfferGen)
-  }
+  def unMatched: Gen[(Set[HousePurchaseOffer], Set[HouseListing])] = Gen.sized {
+    size => for {
+      offers <- Gen.containerOfN[Set, HousePurchaseOffer](size, housePurchaseOffer)
+      listing <- Gen.containerOfN[Set, HouseListing](size, houseListing)
+    } yield (offers, listing)
 
-  val houseListings: Gen[HashSet[HouseListing]] = Gen.sized {
-    n => Gen.containerOfN[HashSet, HouseListing](n, houseListingGen)
   }
 
-  property("matching should be incentive-compatible") = Prop.forAll(housePurchaseOffers, houseListings) {
-    case (offers, listings) =>
-      val ((_, _), matching) = (new DeferredAcceptanceAlgorithm[HousePurchaseOffer, HouseListing])(offers, listings)
-      matching.matches.forall{ case (offer, listing) => offer.price >= listing.price }
+  property("matching should be incentive-compatible") = Prop.forAll(unMatched) { unmatched =>
+        val result = State(new DeferredAcceptanceAlgorithm[HousePurchaseOffer, HouseListing]).run(unmatched)
+        val ((_, _), matching) = result.value
+        matching.matches.forall{ case (offer, listing) => offer.price >= listing.price }
   }
 
-  property("matching should be stable") =  Prop.forAll(housePurchaseOffers, houseListings) {
-    case (offers, listings) =>
-      val ((_, _), matching) = (new DeferredAcceptanceAlgorithm[HousePurchaseOffer, HouseListing])(offers, listings)
-      offers.forall(o => listings.forall(l => !matching.isBlockedBy(l -> o)))
+  property("matching should be stable") =  Prop.forAll(unMatched) { unmatched =>
+    val result = State(new DeferredAcceptanceAlgorithm[HousePurchaseOffer, HouseListing]).run(unmatched)
+    val ((_, _), matching) = result.value
+    val (offers, listings) = unmatched
+    offers.forall(o => listings.forall(l => !matching.isBlockedBy(l -> o)))
   }
 
 }
diff --git a/src/functional/scala/org/economicsl/matching/HousePurchaseOffer.scala b/src/functional/scala/org/economicsl/matching/HousePurchaseOffer.scala
index 1810c35..e927b02 100644
--- a/src/functional/scala/org/economicsl/matching/HousePurchaseOffer.scala
+++ b/src/functional/scala/org/economicsl/matching/HousePurchaseOffer.scala
@@ -20,7 +20,7 @@ import java.util.UUID
 import org.economicsl.core.Price
 
 
-case class HousePurchaseOffer(uuid: UUID, issuer: Long, price: Price)
+case class HousePurchaseOffer(uuid: UUID, issuer: UUID, price: Price)
   extends Proposer with Predicate[HouseListing] with Preferences[HouseListing] {
 
   /** Boolean function used to determine whether some `HouseListing` is acceptable.
diff --git a/src/main/scala/org/economicsl/matching/manytoone/DeferredAcceptanceAlgorithm.scala b/src/main/scala/org/economicsl/matching/manytoone/DeferredAcceptanceAlgorithm.scala
index f8d814d..f238197 100644
--- a/src/main/scala/org/economicsl/matching/manytoone/DeferredAcceptanceAlgorithm.scala
+++ b/src/main/scala/org/economicsl/matching/manytoone/DeferredAcceptanceAlgorithm.scala
@@ -27,67 +27,68 @@ import scala.collection.immutable.TreeSet
   */
 class DeferredAcceptanceAlgorithm[M <: Proposer with Predicate[W] with Preferences[W],
                                   W <: Predicate[M] with Preferences[M] with Quota]
-  extends ((Set[M], Set[W]) => ((Set[M], Set[W]), ManyToOneMatching[W, M])) {
+    extends (((Set[M], Set[W])) => ((Set[M], Set[W]), ManyToOneMatching[W, M])) {
 
-    /** Compute a stable matching between two sets.
-      *
-      * @param ms set of proposers to be matched.
-      * @param ws set of proposees to be matched.
-      * @return
-      * @note A matching will be called "stable" unless there is a pair each of which strictly prefers the other
-      *       to its partner in the matching. This algorithm produces a weakly stable matching in `O(n^2)` time where `n`
-      *       is the size of the inputs sets.
-      */
-    def apply(ms: Set[M], ws: Set[W]): ((Set[M], Set[W]), ManyToOneMatching[W, M]) = {
+  /** Compute a stable matching between two sets.
+    *
+    * @param unmatched
+    * @return
+    * @note A matching will be called "stable" unless there is a pair each of which strictly prefers the other
+    *       to its partner in the matching. This algorithm produces a weakly stable matching in `O(n^2)` time where `n`
+    *       is the size of the inputs sets.
+    */
+  def apply(unmatched: (Set[M], Set[W])): ((Set[M], Set[W]), ManyToOneMatching[W, M]) = {
+    val (ms, ws) = unmatched
 
-      @annotation.tailrec
-      def accumulate(unMatched: Set[M], toBeMatched: Set[M], matches: Map[W, TreeSet[M]], rejected: Map[M, Set[W]]): (Set[M], Set[W], Map[W, TreeSet[M]]) = {
-        toBeMatched.headOption match {
-          case Some(toBeMatchedM) =>
-            val previouslyRejected = rejected.getOrElse(toBeMatchedM, Set.empty)
-            val acceptableWs = ws.diff(previouslyRejected)
-            if (acceptableWs.isEmpty) {
-              accumulate(unMatched + toBeMatchedM, toBeMatched - toBeMatchedM, matches, rejected)
-            } else {
-              val mostPreferredW = acceptableWs.max(toBeMatchedM.ordering)
-              matches.get(mostPreferredW) match {
-                case Some(matchedMs) if mostPreferredW.isAcceptable(toBeMatchedM) =>
-                  matchedMs.headOption match {
-                    case Some(_) if matchedMs.size < mostPreferredW.quota =>
-                      val updatedToBeMatchedMs = toBeMatched - toBeMatchedM
-                      val updatedMatches = matches.updated(mostPreferredW, matchedMs + toBeMatchedM)
-                      accumulate(unMatched, updatedToBeMatchedMs, updatedMatches, rejected)
-                    case Some(leastPreferredMatchedM) if mostPreferredW.ordering.lt(leastPreferredMatchedM, toBeMatchedM) =>
-                      val updatedToBeMatchedMs = toBeMatched - toBeMatchedM + leastPreferredMatchedM
-                      val updatedMatches = matches.updated(mostPreferredW, matchedMs - leastPreferredMatchedM + toBeMatchedM)
-                      val updatedRejected = rejected.updated(leastPreferredMatchedM, rejected.getOrElse(leastPreferredMatchedM, Set.empty) + mostPreferredW)
-                      accumulate(unMatched, updatedToBeMatchedMs, updatedMatches, updatedRejected)
-                    case Some(leastPreferredMatchedM) if mostPreferredW.ordering.gteq(leastPreferredMatchedM, toBeMatchedM) =>
-                      val updatedRejected = rejected.updated(toBeMatchedM, previouslyRejected + mostPreferredW)
-                      accumulate(unMatched, toBeMatched, matches, updatedRejected)
-                    case None =>
-                      val updatedToBeMatchedMs = toBeMatched - toBeMatchedM
-                      val updatedMatches = matches.updated(mostPreferredW, matchedMs + toBeMatchedM)
-                      accumulate(unMatched, updatedToBeMatchedMs, updatedMatches, rejected)
-                  }
-                case Some(_) if mostPreferredW.isNotAcceptable(toBeMatchedM) =>
-                  val updatedRejected = rejected.updated(toBeMatchedM, previouslyRejected + mostPreferredW)
-                  accumulate(unMatched, toBeMatched, matches, updatedRejected)
-                case None if mostPreferredW.isAcceptable(toBeMatchedM) =>
-                  val updatedMatches = matches + (mostPreferredW -> TreeSet(toBeMatchedM)(mostPreferredW.ordering))
-                  accumulate(unMatched, toBeMatched - toBeMatchedM, updatedMatches, rejected)
-                case None if mostPreferredW.isNotAcceptable(toBeMatchedM) =>
-                  val updatedRejected = rejected.updated(toBeMatchedM, previouslyRejected + mostPreferredW)
-                  accumulate(unMatched, toBeMatched, matches, updatedRejected)
-              }
+    @annotation.tailrec
+    def accumulate(unMatched: Set[M], toBeMatched: Set[M], matches: Map[W, TreeSet[M]], rejected: Map[M, Set[W]]): (Set[M], Set[W], Map[W, TreeSet[M]]) = {
+      toBeMatched.headOption match {
+        case Some(toBeMatchedM) =>
+          val previouslyRejected = rejected.getOrElse(toBeMatchedM, Set.empty)
+          val acceptableWs = ws.diff(previouslyRejected)
+          if (acceptableWs.isEmpty) {
+            accumulate(unMatched + toBeMatchedM, toBeMatched - toBeMatchedM, matches, rejected)
+          } else {
+            val mostPreferredW = acceptableWs.max(toBeMatchedM.ordering)
+            matches.get(mostPreferredW) match {
+              case Some(matchedMs) if mostPreferredW.isAcceptable(toBeMatchedM) =>
+                matchedMs.headOption match {
+                  case Some(_) if matchedMs.size < mostPreferredW.quota =>
+                    val updatedToBeMatchedMs = toBeMatched - toBeMatchedM
+                    val updatedMatches = matches.updated(mostPreferredW, matchedMs + toBeMatchedM)
+                    accumulate(unMatched, updatedToBeMatchedMs, updatedMatches, rejected)
+                  case Some(leastPreferredMatchedM) if mostPreferredW.ordering.lt(leastPreferredMatchedM, toBeMatchedM) =>
+                    val updatedToBeMatchedMs = toBeMatched - toBeMatchedM + leastPreferredMatchedM
+                    val updatedMatches = matches.updated(mostPreferredW, matchedMs - leastPreferredMatchedM + toBeMatchedM)
+                    val updatedRejected = rejected.updated(leastPreferredMatchedM, rejected.getOrElse(leastPreferredMatchedM, Set.empty) + mostPreferredW)
+                    accumulate(unMatched, updatedToBeMatchedMs, updatedMatches, updatedRejected)
+                  case Some(leastPreferredMatchedM) if mostPreferredW.ordering.gteq(leastPreferredMatchedM, toBeMatchedM) =>
+                    val updatedRejected = rejected.updated(toBeMatchedM, previouslyRejected + mostPreferredW)
+                    accumulate(unMatched, toBeMatched, matches, updatedRejected)
+                  case None =>
+                    val updatedToBeMatchedMs = toBeMatched - toBeMatchedM
+                    val updatedMatches = matches.updated(mostPreferredW, matchedMs + toBeMatchedM)
+                    accumulate(unMatched, updatedToBeMatchedMs, updatedMatches, rejected)
+                }
+              case Some(_) if mostPreferredW.isNotAcceptable(toBeMatchedM) =>
+                val updatedRejected = rejected.updated(toBeMatchedM, previouslyRejected + mostPreferredW)
+                accumulate(unMatched, toBeMatched, matches, updatedRejected)
+              case None if mostPreferredW.isAcceptable(toBeMatchedM) =>
+                val updatedMatches = matches + (mostPreferredW -> TreeSet(toBeMatchedM)(mostPreferredW.ordering))
+                accumulate(unMatched, toBeMatched - toBeMatchedM, updatedMatches, rejected)
+              case None if mostPreferredW.isNotAcceptable(toBeMatchedM) =>
+                val updatedRejected = rejected.updated(toBeMatchedM, previouslyRejected + mostPreferredW)
+                accumulate(unMatched, toBeMatched, matches, updatedRejected)
             }
-          case None =>
-            (unMatched, matches.keySet.diff(ws), matches)
-        }
+          }
+        case None =>
+          (unMatched, matches.keySet.diff(ws), matches)
       }
-      val unacceptableWs = ms.foldLeft(Map.empty[M, Set[W]])((z, m) => z + (m -> ws.filter(m.isAcceptable)))
-      val (unMatchedMs, unMatchedWs, matches) = accumulate(Set.empty, ms, Map.empty, unacceptableWs)
-      ((unMatchedMs, unMatchedWs), ManyToOneMatching(matches))
     }
 
+    val unacceptableWs = ms.foldLeft(Map.empty[M, Set[W]])((z, m) => z + (m -> ws.filter(m.isAcceptable)))
+    val (unMatchedMs, unMatchedWs, matches) = accumulate(Set.empty, ms, Map.empty, unacceptableWs)
+    ((unMatchedMs, unMatchedWs), ManyToOneMatching(matches))
   }
+
+}
diff --git a/src/main/scala/org/economicsl/matching/onetoone/DeferredAcceptanceAlgorithm.scala b/src/main/scala/org/economicsl/matching/onetoone/DeferredAcceptanceAlgorithm.scala
index 9da8091..9cbfb9e 100644
--- a/src/main/scala/org/economicsl/matching/onetoone/DeferredAcceptanceAlgorithm.scala
+++ b/src/main/scala/org/economicsl/matching/onetoone/DeferredAcceptanceAlgorithm.scala
@@ -17,24 +17,25 @@ package org.economicsl.matching.onetoone
 
 import org.economicsl.matching.{Predicate, Preferences, Proposer}
 
+
 /** Class implementing the deferred acceptance algorithm.
   *
   * @tparam M the type of proposer.
   * @tparam W the type of proposee.
   */
 class DeferredAcceptanceAlgorithm[M <: Proposer with Predicate[W] with Preferences[W], W <: Predicate[M] with Preferences[M]]
-  extends ((Set[M], Set[W]) => ((Set[M], Set[W]), OneToOneMatching[W, M])) {
+  extends (((Set[M], Set[W])) => ((Set[M], Set[W]), OneToOneMatching[W, M])) {
 
   /** Compute a weakly stable matching between two sets.
     *
-    * @param ms set of proposers to be matched.
-    * @param ws set of proposees to be matched.
+    * @param unmatched
     * @return
     * @note A matching will be called "weakly stable" unless there is a pair each of which strictly prefers the other
     *       to its partner in the matching. This algorithm produces a weakly stable matching in `O(n^2)` time where `n`
     *       is the size of the inputs sets.
     */
-  def apply(ms: Set[M], ws: Set[W]): ((Set[M], Set[W]), OneToOneMatching[W, M]) = {
+  def apply(unmatched: (Set[M], Set[W])): ((Set[M], Set[W]), OneToOneMatching[W, M]) = {
+    val (ms, ws) = unmatched
 
     @annotation.tailrec
     def accumulate(unMatchedMs: Set[M], toBeMatchedMs: Set[M], matches: Map[W, M], rejected: Map[M, Set[W]]): (Set[M], Set[W], Map[W, M]) = {
diff --git a/src/main/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithm.scala b/src/main/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithm.scala
index 80f300e..8bcb380 100644
--- a/src/main/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithm.scala
+++ b/src/main/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithm.scala
@@ -38,15 +38,15 @@ import scala.util.{Failure, Success, Try}
   *      [[http://www.eecs.harvard.edu/cs286r/courses/fall09/papers/galeshapley.pdf ''Gale and Shapley (1962)'']].
   */
 class StableMarriageAlgorithm[M <: Proposer with Preferences[W], W <: Preferences[M]]
-  extends ((Set[M], Set[W]) => Try[((Set[M], Set[W]), OneToOneMatching[W, M])]) {
+  extends (((Set[M], Set[W])) => ((Set[M], Set[W]), Try[OneToOneMatching[W, M]])) {
 
   /** Compute a stable matching between two sets of equal size.
     *
-    * @param ms set of proposers to be matched.
-    * @param ws set of proposees to be matched.
+    * @param unmatched
     * @return a stable matching between proposees (`ws`) and proposers (`ms`).
     */
-  def apply(ms: Set[M], ws: Set[W]): Try[((Set[M], Set[W]), OneToOneMatching[W, M])] = {
+  def apply(unmatched: (Set[M], Set[W])): ((Set[M], Set[W]), Try[OneToOneMatching[W, M]]) = {
+    val (ms, ws) = unmatched
 
     @annotation.tailrec
     def accumulate(unMatchedMs: Set[M], matches: Map[W, M], rejected: Map[M, Set[W]]): (Set[M], Set[W], Map[W, M]) = {
@@ -74,10 +74,10 @@ class StableMarriageAlgorithm[M <: Proposer with Preferences[W], W <: Preference
 
     if (ms.size == ws.size) {
       val (unMatchedMs, unMatchedWs, matches) = accumulate(ms, Map.empty, Map.empty)
-      Success(((unMatchedMs, unMatchedWs), OneToOneMatching(matches)))
+      ((unMatchedMs, unMatchedWs), Success(OneToOneMatching(matches)))
     }
     else {
-      Failure(new IllegalArgumentException(s"The size of ms is ${ms.size} which does not equal the size of ws which is ${ws.size}!"))
+      ((ms, ws), Failure(new IllegalArgumentException(s"The size of ms is ${ms.size} which does not equal the size of ws which is ${ws.size}!")))
     }
 
   }
diff --git a/src/performance/scala/org/economicsl/matching/DeferredAcceptanceMicroBenchmark.scala b/src/performance/scala/org/economicsl/matching/DeferredAcceptanceMicroBenchmark.scala
index be05c03..da0f674 100644
--- a/src/performance/scala/org/economicsl/matching/DeferredAcceptanceMicroBenchmark.scala
+++ b/src/performance/scala/org/economicsl/matching/DeferredAcceptanceMicroBenchmark.scala
@@ -19,11 +19,11 @@ object DeferredAcceptanceMicroBenchmark extends Bench.OnlineRegressionReport {
   }
 
   def randomHouseListing(): HouseListing = {
-    HouseListing(UUID.randomUUID(), Random.nextLong(), Price(Random.nextLong()), randomHouse())
+    HouseListing(UUID.randomUUID(), UUID.randomUUID(), Price(Random.nextLong()), randomHouse())
   }
 
   def randomHousePurchaseOffer(): HousePurchaseOffer = {
-    HousePurchaseOffer(UUID.randomUUID(), Random.nextLong(), Price(Random.nextLong()))
+    HousePurchaseOffer(UUID.randomUUID(), UUID.randomUUID(), Price(Random.nextLong()))
   }
 
   def randomHousePurchaseOffers(size: Int): HashSet[HousePurchaseOffer] = {
@@ -66,8 +66,8 @@ object DeferredAcceptanceMicroBenchmark extends Bench.OnlineRegressionReport {
 //    }
 
     measure method "weaklyStableMatching" in {
-      using(unMatchedParticipants) in { case (buyers, sellers) =>
-        (new StableMarriageAlgorithm[HousePurchaseOffer, HouseListing]())(buyers, sellers)
+      using(unMatchedParticipants) in { unmatched =>
+        (new StableMarriageAlgorithm[HousePurchaseOffer, HouseListing]())(unmatched)
       }
     }
 
diff --git a/src/test/scala/org/economicsl/matching/manytoone/SchoolChoiceSpecification.scala b/src/test/scala/org/economicsl/matching/manytoone/SchoolChoiceSpecification.scala
index 3f834a2..15d6fab 100644
--- a/src/test/scala/org/economicsl/matching/manytoone/SchoolChoiceSpecification.scala
+++ b/src/test/scala/org/economicsl/matching/manytoone/SchoolChoiceSpecification.scala
@@ -15,6 +15,7 @@ limitations under the License.
 */
 package org.economicsl.matching.manytoone
 
+import cats.data.State
 import org.scalacheck.{Gen, Prop, Properties}
 
 
@@ -45,14 +46,17 @@ object SchoolChoiceSpecification extends Properties("school-choice") {
   }
 
   property("no school accepts more students than its quota allows") = Prop.forAll(unMatched) {
-    case (students, schools) =>
-      val ((_, _), matching) = (new DeferredAcceptanceAlgorithm[Student, School])(students, schools)
+    unmatched =>
+      val result = State(new DeferredAcceptanceAlgorithm[Student, School]).run(unmatched)
+      val ((_, _), matching)= result.value
       matching.matches.forall{ case (school, matchedStudents) => matchedStudents.size <= school.quota }
   }
 
   property("matching should be stable") = Prop.forAll(unMatched) {
-    case (students, schools) =>
-      val ((_, _), matching) = (new DeferredAcceptanceAlgorithm[Student, School])(students, schools)
+    unmatched =>
+      val result = State(new DeferredAcceptanceAlgorithm[Student, School]).run(unmatched)
+      val ((_, _), matching)= result.value
+      val (students, schools) = unmatched
       students.forall(student => schools.forall(school => !matching.isBlockedBy(school -> student)))
   }
 
diff --git a/src/test/scala/org/economicsl/matching/onetoone/MarriageMarketSpecification.scala b/src/test/scala/org/economicsl/matching/onetoone/MarriageMarketSpecification.scala
index 64a8119..2da934a 100644
--- a/src/test/scala/org/economicsl/matching/onetoone/MarriageMarketSpecification.scala
+++ b/src/test/scala/org/economicsl/matching/onetoone/MarriageMarketSpecification.scala
@@ -15,6 +15,8 @@ limitations under the License.
 */
 package org.economicsl.matching.onetoone
 
+
+import cats.data.State
 import org.scalacheck.{Gen, Prop, Properties}
 
 import scala.util.{Failure, Success}
@@ -46,22 +48,24 @@ object MarriageMarketSpecification extends Properties("marriage-market") {
   }
 
   property("all men and women are matched") = Prop.forAll(randomUnmatchedSets) {
-    case (ms, ws) =>
-      val result = (new StableMarriageAlgorithm[Man, Woman])(ms, ws)
-      result match {
-        case Success(((unMatchedMs, unMatchedWs), matching)) =>
-          (ms.size == ws.size) && unMatchedMs.isEmpty && unMatchedWs.isEmpty && (matching.size == ms.size)
+    case unmatched @ (ms, ws) =>
+      val result = State(new StableMarriageAlgorithm[Man, Woman]).run(unmatched)
+      val ((unMatchedMs, unMatchedWs), matching) = result.value
+      matching match {
+        case Success(oneToOneMatching) =>
+          (ms.size == ws.size) && unMatchedMs.isEmpty && unMatchedWs.isEmpty && (oneToOneMatching.size == ms.size)
         case Failure(_) =>
           ms.size != ws.size
       }
   }
 
   property("matching should be stable") = Prop.forAll(randomUnmatchedSets) {
-    case (ms, ws) =>
-      val result = (new StableMarriageAlgorithm[Man, Woman])(ms, ws)
-      result match {
-        case Success(((_, _), matching)) =>
-          ms.forall(m => ws.forall(w => !matching.isBlockedBy(w -> m)))
+    case unmatched @ (ms, ws) =>
+      val result = State(new StableMarriageAlgorithm[Man, Woman]).run(unmatched)
+      val ((_, _), matching) = result.value
+      matching match {
+        case Success(oneToOneMatching) =>
+          ms.forall(m => ws.forall(w => !oneToOneMatching.isBlockedBy(w -> m)))
         case Failure(_) =>
           ms.size != ws.size
       }
diff --git a/src/test/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithmSpec.scala b/src/test/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithmSpec.scala
index 7c88de6..e28ba59 100644
--- a/src/test/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithmSpec.scala
+++ b/src/test/scala/org/economicsl/matching/onetoone/StableMarriageAlgorithmSpec.scala
@@ -25,20 +25,23 @@ import scala.util.{Failure, Success}
 class StableMarriageAlgorithmSpec extends FlatSpec {
 
   "The stable marriage algorithm applied to two empty sets" should "successfully return an empty matching." in {
-    val result = (new StableMarriageAlgorithm[Man, Woman])(Set.empty[Man], Set.empty[Woman])
+    val unmatched = (Set.empty[Man], Set.empty[Woman])
+    val result = (new StableMarriageAlgorithm[Man, Woman])(unmatched)
     result match {
-      case Success(((_, _), matching)) =>
+      case ((_, _), Success(matching)) =>
         assert(matching.isEmpty)
-      case Failure(_) =>
+      case ((_,_), Failure(_)) =>
         false
     }
   }
 
   "The stable matching algorithm applied to sets of different sizes" should "return a failure." in {
-    val result1 = (new StableMarriageAlgorithm[Man, Woman])(Set(Man(UUID.randomUUID(), 42, Man.womanByQuality)), Set.empty[Woman])
+    val unmatched1 = (Set(Man(UUID.randomUUID(), 42, Man.womanByQuality)), Set.empty[Woman])
+    val ((_, _), result1) = (new StableMarriageAlgorithm[Man, Woman])(unmatched1)
     assert(result1.isFailure)
 
-    val result2 = (new StableMarriageAlgorithm[Man, Woman])(Set.empty[Man], Set(Woman(UUID.randomUUID(), 42, Woman.manByQuality)))
+    val unmatched2 = (Set.empty[Man], Set(Woman(UUID.randomUUID(), 42, Woman.manByQuality)))
+    val ((_, _), result2) = (new StableMarriageAlgorithm[Man, Woman])(unmatched2)
     assert(result2.isFailure)
   }