diff --git a/src/i_introduction/_0_Hello_World/n00Start.kt b/src/i_introduction/_0_Hello_World/n00Start.kt
index 352ca5bfc..1850528c2 100644
--- a/src/i_introduction/_0_Hello_World/n00Start.kt
+++ b/src/i_introduction/_0_Hello_World/n00Start.kt
@@ -24,6 +24,4 @@ fun todoTask0(): Nothing = TODO(
     references = { task0(); "OK" }
 )
 
-fun task0(): String {
-    return todoTask0()
-}
\ No newline at end of file
+fun task0() = "OK"
\ No newline at end of file
diff --git a/src/i_introduction/_10_Object_Expressions/n10ObjectExpressions.kt b/src/i_introduction/_10_Object_Expressions/n10ObjectExpressions.kt
index ef12d8127..235766dc2 100644
--- a/src/i_introduction/_10_Object_Expressions/n10ObjectExpressions.kt
+++ b/src/i_introduction/_10_Object_Expressions/n10ObjectExpressions.kt
@@ -18,6 +18,8 @@ fun todoTask10(): Nothing = TODO(
 
 fun task10(): List<Int> {
     val arrayList = arrayListOf(1, 5, 2)
-    Collections.sort(arrayList, todoTask10())
+    Collections.sort(arrayList, object : Comparator<Int> {
+        override fun compare(x: Int, y: Int) = y - x
+    })
     return arrayList
 }
\ No newline at end of file
diff --git a/src/i_introduction/_11_SAM_Conversions/n11SAMConversions.kt b/src/i_introduction/_11_SAM_Conversions/n11SAMConversions.kt
index 5f021921c..68a3dd5bc 100644
--- a/src/i_introduction/_11_SAM_Conversions/n11SAMConversions.kt
+++ b/src/i_introduction/_11_SAM_Conversions/n11SAMConversions.kt
@@ -15,6 +15,6 @@ fun todoTask11(): Nothing = TODO(
 
 fun task11(): List<Int> {
     val arrayList = arrayListOf(1, 5, 2)
-    Collections.sort(arrayList, { x, y -> todoTask11() })
+    Collections.sort(arrayList, { x, y -> y - x })
     return arrayList
 }
diff --git a/src/i_introduction/_12_Extensions_On_Collections/n12ExtensionsOnCollections.kt b/src/i_introduction/_12_Extensions_On_Collections/n12ExtensionsOnCollections.kt
index ae453a63b..dac9162a2 100644
--- a/src/i_introduction/_12_Extensions_On_Collections/n12ExtensionsOnCollections.kt
+++ b/src/i_introduction/_12_Extensions_On_Collections/n12ExtensionsOnCollections.kt
@@ -17,7 +17,6 @@ fun todoTask12(): Nothing = TODO(
 )
 
 fun task12(): List<Int> {
-    todoTask12()
-    return arrayListOf(1, 5, 2)
+    return arrayListOf(1, 5, 2).sortedDescending()
 }
 
diff --git a/src/i_introduction/_1_Java_To_Kotlin_Converter/n01JavaToKotlinConverter.kt b/src/i_introduction/_1_Java_To_Kotlin_Converter/n01JavaToKotlinConverter.kt
index f7a40f5e8..bcab8face 100644
--- a/src/i_introduction/_1_Java_To_Kotlin_Converter/n01JavaToKotlinConverter.kt
+++ b/src/i_introduction/_1_Java_To_Kotlin_Converter/n01JavaToKotlinConverter.kt
@@ -14,5 +14,16 @@ fun todoTask1(collection: Collection<Int>): Nothing = TODO(
 
 
 fun task1(collection: Collection<Int>): String {
-    todoTask1(collection)
+    val sb = StringBuilder()
+    sb.append("{")
+    val iterator = collection.iterator()
+    while (iterator.hasNext()) {
+        val element = iterator.next()
+        sb.append(element)
+        if (iterator.hasNext()) {
+            sb.append(", ")
+        }
+    }
+    sb.append("}")
+    return sb.toString()
 }
\ No newline at end of file
diff --git a/src/i_introduction/_2_Named_Arguments/n02NamedArguments.kt b/src/i_introduction/_2_Named_Arguments/n02NamedArguments.kt
index 11fc442bb..b1dd036f4 100644
--- a/src/i_introduction/_2_Named_Arguments/n02NamedArguments.kt
+++ b/src/i_introduction/_2_Named_Arguments/n02NamedArguments.kt
@@ -24,6 +24,5 @@ fun todoTask2(): Nothing = TODO(
     references = { collection: Collection<Int> -> task1(collection); collection.joinToString() })
 
 fun task2(collection: Collection<Int>): String {
-    todoTask2()
-    return collection.joinToString()
+    return collection.joinToString(prefix = "{", postfix = "}")
 }
\ No newline at end of file
diff --git a/src/i_introduction/_3_Default_Arguments/n03DefaultArguments.kt b/src/i_introduction/_3_Default_Arguments/n03DefaultArguments.kt
index b7adbd670..25100c70b 100644
--- a/src/i_introduction/_3_Default_Arguments/n03DefaultArguments.kt
+++ b/src/i_introduction/_3_Default_Arguments/n03DefaultArguments.kt
@@ -14,12 +14,12 @@ fun todoTask3(): Nothing = TODO(
     documentation = doc2(),
     references = { name: String -> JavaCode3().foo(name); foo(name) })
 
-fun foo(name: String): String = todoTask3()
+fun foo(name: String, number: Int = 42, toUpperCase: Boolean = false) =
+        (if (toUpperCase) name.toUpperCase() else name) + number
 
 fun task3(): String {
-    todoTask3()
-//    return (foo("a") +
-//            foo("b", number = 1) +
-//            foo("c", toUpperCase = true) +
-//            foo(name = "d", number = 2, toUpperCase = true))
+    return (foo("a") +
+            foo("b", number = 1) +
+            foo("c", toUpperCase = true) +
+            foo(name = "d", number = 2, toUpperCase = true))
 }
\ No newline at end of file
diff --git a/src/i_introduction/_4_Lambdas/n04Lambdas.kt b/src/i_introduction/_4_Lambdas/n04Lambdas.kt
index 3c174fc77..4a3d7e070 100644
--- a/src/i_introduction/_4_Lambdas/n04Lambdas.kt
+++ b/src/i_introduction/_4_Lambdas/n04Lambdas.kt
@@ -22,4 +22,4 @@ fun todoTask4(collection: Collection<Int>): Nothing = TODO(
     documentation = doc4(),
     references = { JavaCode4().task4(collection) })
 
-fun task4(collection: Collection<Int>): Boolean = todoTask4(collection)
\ No newline at end of file
+fun task4(collection: Collection<Int>): Boolean = collection.any { it % 2 == 0 }
\ No newline at end of file
diff --git a/src/i_introduction/_5_String_Templates/n05StringTemplates.kt b/src/i_introduction/_5_String_Templates/n05StringTemplates.kt
index 7b7f9b625..05dbaf086 100644
--- a/src/i_introduction/_5_String_Templates/n05StringTemplates.kt
+++ b/src/i_introduction/_5_String_Templates/n05StringTemplates.kt
@@ -35,4 +35,4 @@ fun todoTask5(): Nothing = TODO(
     documentation = doc5(),
     references = { getPattern(); month })
 
-fun task5(): String = todoTask5()
+fun task5(): String = """\d{2} $month \d{4}"""
\ No newline at end of file
diff --git a/src/i_introduction/_6_Data_Classes/n06DataClasses.kt b/src/i_introduction/_6_Data_Classes/n06DataClasses.kt
index 1ce6b8796..6b5a46f9a 100644
--- a/src/i_introduction/_6_Data_Classes/n06DataClasses.kt
+++ b/src/i_introduction/_6_Data_Classes/n06DataClasses.kt
@@ -15,10 +15,10 @@ fun todoTask6(): Nothing = TODO(
     references = { JavaCode6.Person("Alice", 29) }
 )
 
-class Person
+data class Person(val name: String, val age: Int)
 
 fun task6(): List<Person> {
-    todoTask6()
-    return listOf(/*Person("Alice", 29), Person("Bob", 31)*/)
+//    todoTask6()
+    return listOf(Person("Alice", 29), Person("Bob", 31))
 }
 
diff --git a/src/i_introduction/_7_Nullable_Types/n07NullableTypes.kt b/src/i_introduction/_7_Nullable_Types/n07NullableTypes.kt
index 1d0109436..77a79a3e8 100644
--- a/src/i_introduction/_7_Nullable_Types/n07NullableTypes.kt
+++ b/src/i_introduction/_7_Nullable_Types/n07NullableTypes.kt
@@ -25,7 +25,13 @@ fun todoTask7(client: Client?, message: String?, mailer: Mailer): Nothing = TODO
 fun sendMessageToClient(
     client: Client?, message: String?, mailer: Mailer
 ) {
-    todoTask7(client, message, mailer)
+//    todoTask7(client, message, mailer)
+    val email = client?.personalInfo?.email
+
+    if (email != null && message != null) {
+
+        mailer.sendMessage(email, message)
+    }
 }
 
 class Client(val personalInfo: PersonalInfo?)
diff --git a/src/i_introduction/_8_Smart_Casts/n08SmartCasts.kt b/src/i_introduction/_8_Smart_Casts/n08SmartCasts.kt
index 6f3a6675e..03ad236fe 100644
--- a/src/i_introduction/_8_Smart_Casts/n08SmartCasts.kt
+++ b/src/i_introduction/_8_Smart_Casts/n08SmartCasts.kt
@@ -12,8 +12,8 @@ class Sum(val left: Expr, val right: Expr) : Expr()
 
 fun eval(e: Expr): Int =
     when (e) {
-        is Num -> todoTask8(e)
-        is Sum -> todoTask8(e)
+        is Num -> e.value
+        is Sum -> eval(e.left) + eval(e.right)
     }
 
 fun todoTask8(expr: Expr): Nothing = TODO(
diff --git a/src/i_introduction/_9_Extension_Functions/n09ExtensionFunctions.kt b/src/i_introduction/_9_Extension_Functions/n09ExtensionFunctions.kt
index 75506f232..dc831e29e 100644
--- a/src/i_introduction/_9_Extension_Functions/n09ExtensionFunctions.kt
+++ b/src/i_introduction/_9_Extension_Functions/n09ExtensionFunctions.kt
@@ -29,7 +29,7 @@ fun todoTask9(): Nothing = TODO(
 
 data class RationalNumber(val numerator: Int, val denominator: Int)
 
-fun Int.r(): RationalNumber = todoTask9()
-fun Pair<Int, Int>.r(): RationalNumber = todoTask9()
+fun Int.r(): RationalNumber = RationalNumber(this, 1)
+fun Pair<Int, Int>.r(): RationalNumber = RationalNumber(this.first, this.second)
 
 
diff --git a/src/ii_collections/n13Introduction.kt b/src/ii_collections/n13Introduction.kt
index 6a67983c8..32f8fe4b0 100644
--- a/src/ii_collections/n13Introduction.kt
+++ b/src/ii_collections/n13Introduction.kt
@@ -18,7 +18,6 @@ fun example0(list: List<Int>) {
 
 fun Shop.getSetOfCustomers(): Set<Customer> {
     // Return a set containing all the customers of this shop
-    todoCollectionTask()
-//    return this.customers
+    return customers.toSet()
 }
 
diff --git a/src/ii_collections/n14FilterMap.kt b/src/ii_collections/n14FilterMap.kt
index c547b44b6..4a45002e3 100644
--- a/src/ii_collections/n14FilterMap.kt
+++ b/src/ii_collections/n14FilterMap.kt
@@ -10,12 +10,12 @@ fun example1(list: List<Int>) {
 
 fun Shop.getCitiesCustomersAreFrom(): Set<City> {
     // Return the set of cities the customers are from
-    todoCollectionTask()
+    return customers.map { it.city }.toSet()
 }
 
 fun Shop.getCustomersFrom(city: City): List<Customer> {
     // Return a list of the customers who live in the given city
-    todoCollectionTask()
+    return customers.filter { it.city == city }
 }
 
 
diff --git a/src/ii_collections/n15AllAnyAndOtherPredicates.kt b/src/ii_collections/n15AllAnyAndOtherPredicates.kt
index 15b417317..c3e7ae128 100644
--- a/src/ii_collections/n15AllAnyAndOtherPredicates.kt
+++ b/src/ii_collections/n15AllAnyAndOtherPredicates.kt
@@ -15,25 +15,26 @@ fun example2(list: List<Int>) {
 
 fun Customer.isFrom(city: City): Boolean {
     // Return true if the customer is from the given city
-    todoCollectionTask()
+    return this.city == city
 }
 
 fun Shop.checkAllCustomersAreFrom(city: City): Boolean {
     // Return true if all customers are from the given city
-    todoCollectionTask()
+    return customers.all { it.isFrom(city) }
 }
 
 fun Shop.hasCustomerFrom(city: City): Boolean {
     // Return true if there is at least one customer from the given city
-    todoCollectionTask()
+    return customers.any { it.isFrom(city) }
 }
 
 fun Shop.countCustomersFrom(city: City): Int {
     // Return the number of customers from the given city
-    todoCollectionTask()
+    return customers.count { it.isFrom(city) }
 }
 
 fun Shop.findFirstCustomerFrom(city: City): Customer? {
     // Return the first customer who lives in the given city, or null if there is none
-    todoCollectionTask()
+    return customers.firstOrNull { it.isFrom(city) }
 }
+
diff --git a/src/ii_collections/n16FlatMap.kt b/src/ii_collections/n16FlatMap.kt
index 22f9b92f4..73c1c1445 100644
--- a/src/ii_collections/n16FlatMap.kt
+++ b/src/ii_collections/n16FlatMap.kt
@@ -10,11 +10,11 @@ fun example() {
 val Customer.orderedProducts: Set<Product>
     get() {
         // Return all products this customer has ordered
-        todoCollectionTask()
+        return orders.flatMap { it.products }.toSet()
     }
 
 val Shop.allOrderedProducts: Set<Product>
     get() {
         // Return all products that were ordered by at least one customer
-        todoCollectionTask()
+        return customers.flatMap { it.orderedProducts }.toSet()
     }
diff --git a/src/ii_collections/n17MaxMin.kt b/src/ii_collections/n17MaxMin.kt
index 78b09060b..01feb93d4 100644
--- a/src/ii_collections/n17MaxMin.kt
+++ b/src/ii_collections/n17MaxMin.kt
@@ -7,10 +7,10 @@ fun example4() {
 
 fun Shop.getCustomerWithMaximumNumberOfOrders(): Customer? {
     // Return a customer whose order count is the highest among all customers
-    todoCollectionTask()
+    return customers.maxBy { it.orders.size }
 }
 
 fun Customer.getMostExpensiveOrderedProduct(): Product? {
     // Return the most expensive product which has been ordered
-    todoCollectionTask()
+    return orderedProducts.maxBy { it.price }
 }
diff --git a/src/ii_collections/n18Sort.kt b/src/ii_collections/n18Sort.kt
index 1bbbe4887..4c3a92aad 100644
--- a/src/ii_collections/n18Sort.kt
+++ b/src/ii_collections/n18Sort.kt
@@ -8,5 +8,5 @@ fun example5() {
 
 fun Shop.getCustomersSortedByNumberOfOrders(): List<Customer> {
     // Return a list of customers, sorted by the ascending number of orders they made
-    todoCollectionTask()
+    return customers.sortedBy { it.orders.size }
 }
diff --git a/src/ii_collections/n19Sum.kt b/src/ii_collections/n19Sum.kt
index bfd89c56b..53a19b0d0 100644
--- a/src/ii_collections/n19Sum.kt
+++ b/src/ii_collections/n19Sum.kt
@@ -8,5 +8,5 @@ fun example6() {
 fun Customer.getTotalOrderPrice(): Double {
     // Return the sum of prices of all products that a customer has ordered.
     // Note: a customer may order the same product several times.
-    todoCollectionTask()
+    return orders.flatMap { it.products }.sumByDouble { it.price }
 }
diff --git a/src/ii_collections/n20GroupBy.kt b/src/ii_collections/n20GroupBy.kt
index dd364ea93..5fcdfed32 100644
--- a/src/ii_collections/n20GroupBy.kt
+++ b/src/ii_collections/n20GroupBy.kt
@@ -8,5 +8,5 @@ fun example7() {
 
 fun Shop.groupCustomersByCity(): Map<City, List<Customer>> {
     // Return a map of the customers living in each city
-    todoCollectionTask()
+    return customers.groupBy { it.city }
 }
diff --git a/src/ii_collections/n21Partition.kt b/src/ii_collections/n21Partition.kt
index f95b0da35..031d6fefe 100644
--- a/src/ii_collections/n21Partition.kt
+++ b/src/ii_collections/n21Partition.kt
@@ -12,5 +12,9 @@ fun example8() {
 
 fun Shop.getCustomersWithMoreUndeliveredOrdersThanDelivered(): Set<Customer> {
     // Return customers who have more undelivered orders than delivered
-    todoCollectionTask()
+    return customers.filter {
+        val (delivered, undelivered) = it.orders.partition { it.isDelivered }
+        undelivered.size > delivered.size
+    }.toSet()
 }
+
diff --git a/src/ii_collections/n22Fold.kt b/src/ii_collections/n22Fold.kt
index 2fd2f2fcb..cfe1d4952 100644
--- a/src/ii_collections/n22Fold.kt
+++ b/src/ii_collections/n22Fold.kt
@@ -15,6 +15,6 @@ fun whatFoldDoes(): Int {
 fun Shop.getSetOfProductsOrderedByEachCustomer(): Set<Product> {
     // Return the set of products that were ordered by each of the customers
     return customers.fold(allOrderedProducts, { orderedByAll, customer ->
-        todoCollectionTask()
+        orderedByAll.intersect(customer.orderedProducts)
     })
 }
diff --git a/src/ii_collections/n23CompoundTasks.kt b/src/ii_collections/n23CompoundTasks.kt
index 35bd7eb7b..0ab5d18bd 100644
--- a/src/ii_collections/n23CompoundTasks.kt
+++ b/src/ii_collections/n23CompoundTasks.kt
@@ -2,17 +2,17 @@ package ii_collections
 
 fun Shop.getCustomersWhoOrderedProduct(product: Product): Set<Customer> {
     // Return the set of customers who ordered the specified product
-    todoCollectionTask()
+    return customers.filter { it.orderedProducts.contains(product) }.toSet()
 }
 
 fun Customer.getMostExpensiveDeliveredProduct(): Product? {
     // Return the most expensive product among all delivered products
     // (use the Order.isDelivered flag)
-    todoCollectionTask()
+    return orders.filter { it.isDelivered }.flatMap { it.products }.maxBy { it.price }
 }
 
 fun Shop.getNumberOfTimesProductWasOrdered(product: Product): Int {
     // Return the number of times the given product was ordered.
     // Note: a customer may order the same product for several times.
-    todoCollectionTask()
+    return customers.flatMap { it.orders }.flatMap { it.products }.count { it == product }
 }
diff --git a/src/ii_collections/n24ExtensionsOnCollections.kt b/src/ii_collections/n24ExtensionsOnCollections.kt
index 3188c180e..dc064821d 100644
--- a/src/ii_collections/n24ExtensionsOnCollections.kt
+++ b/src/ii_collections/n24ExtensionsOnCollections.kt
@@ -12,8 +12,8 @@ fun todoTask24(): Nothing = TODO(
 )
 
 fun doSomethingStrangeWithCollection(collection: Collection<String>): Collection<String>? {
-    val groupsByLength = collection.groupBy { s -> todoTask24() }
+    val groupsByLength = collection.groupBy { s -> s.length }
 
-    return groupsByLength.values.maxBy { group -> todoTask24() }
+    return groupsByLength.values.maxBy { group -> group.size }
 }
 
diff --git a/src/iii_conventions/MyDate.kt b/src/iii_conventions/MyDate.kt
index 147cc3e78..fc51e4a47 100644
--- a/src/iii_conventions/MyDate.kt
+++ b/src/iii_conventions/MyDate.kt
@@ -1,8 +1,32 @@
 package iii_conventions
 
-data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int)
+data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int): Comparable<MyDate> {
+    override fun compareTo(other: MyDate) = when {
+        year != other.year -> year - other.year
+        month != other.month -> month - other.month
+        else -> dayOfMonth - other.dayOfMonth
+    }
+}
+
+operator fun MyDate.rangeTo(other: MyDate) = DateRange(this, other)
+
+class DateRange(
+        override val start: MyDate,
+        override val endInclusive: MyDate
+) : ClosedRange<MyDate>, Iterable<MyDate> {
+    override fun iterator(): Iterator<MyDate> = DateIterator(this)
+    override fun contains(value: MyDate): Boolean = start <= value && value <= endInclusive
+}
 
-operator fun MyDate.rangeTo(other: MyDate): DateRange = todoTask27()
+class DateIterator(val dateRange: DateRange) : Iterator<MyDate> {
+    var current: MyDate = dateRange.start
+    override fun next(): MyDate {
+        val result = current
+        current = current.nextDay()
+        return result
+    }
+    override fun hasNext(): Boolean = current <= dateRange.endInclusive
+}
 
 enum class TimeInterval {
     DAY,
@@ -10,4 +34,8 @@ enum class TimeInterval {
     YEAR
 }
 
-class DateRange(val start: MyDate, val endInclusive: MyDate)
+class RepeatedTimeInterval(val timeInterval: TimeInterval, val number: Int)
+operator fun TimeInterval.times(number: Int) = RepeatedTimeInterval(this, number)
+
+operator fun MyDate.plus(timeInterval: TimeInterval) = addTimeIntervals(timeInterval, 1)
+operator fun MyDate.plus(timeIntervals: RepeatedTimeInterval) = addTimeIntervals(timeIntervals.timeInterval, timeIntervals.number)
diff --git a/src/iii_conventions/n25Comparison.kt b/src/iii_conventions/n25Comparison.kt
index 70d5bec60..402b21cdb 100644
--- a/src/iii_conventions/n25Comparison.kt
+++ b/src/iii_conventions/n25Comparison.kt
@@ -16,7 +16,7 @@ fun todoTask25(): Nothing = TODO(
 )
 
 fun task25(date1: MyDate, date2: MyDate): Boolean {
-    todoTask25()
-//    return date1 < date2
+//    todoTask25()
+    return date1 < date2
 }
 
diff --git a/src/iii_conventions/n26InRange.kt b/src/iii_conventions/n26InRange.kt
index 5a57d2dab..7fa9082a3 100644
--- a/src/iii_conventions/n26InRange.kt
+++ b/src/iii_conventions/n26InRange.kt
@@ -18,6 +18,6 @@ fun todoTask26_(): Nothing = TODO(
 )
 
 fun checkInRange(date: MyDate, first: MyDate, last: MyDate): Boolean {
-    todoTask26_()
-//    return date in DateRange(first, last)
+//    todoTask26_()
+    return date in DateRange(first, last)
 }
diff --git a/src/iii_conventions/n27RangeTo.kt b/src/iii_conventions/n27RangeTo.kt
index bfc4f96c5..72b29571c 100644
--- a/src/iii_conventions/n27RangeTo.kt
+++ b/src/iii_conventions/n27RangeTo.kt
@@ -15,6 +15,6 @@ fun todoTask27(): Nothing = TODO(
 )
 
 fun checkInRange2(date: MyDate, first: MyDate, last: MyDate): Boolean {
-    todoTask27()
-//    return date in first..last
+//    todoTask27()
+    return date in first..last
 }
diff --git a/src/iii_conventions/n28ForLoop.kt b/src/iii_conventions/n28ForLoop.kt
index 1f4369566..d4181cba1 100644
--- a/src/iii_conventions/n28ForLoop.kt
+++ b/src/iii_conventions/n28ForLoop.kt
@@ -37,8 +37,8 @@ fun todoTask28(): Nothing = TODO(
 
 
 fun iterateOverDateRange(firstDate: MyDate, secondDate: MyDate, handler: (MyDate) -> Unit) {
-    todoTask28()
-//    for (date in firstDate..secondDate) {
-//        handler(date)
-//    }
+//    todoTask28()
+    for (date in firstDate..secondDate) {
+        handler(date)
+    }
 }
diff --git a/src/iii_conventions/n29OperatorsOverloading.kt b/src/iii_conventions/n29OperatorsOverloading.kt
index 3f96b416f..69b6ca432 100644
--- a/src/iii_conventions/n29OperatorsOverloading.kt
+++ b/src/iii_conventions/n29OperatorsOverloading.kt
@@ -20,12 +20,12 @@ fun todoTask29(): Nothing = TODO(
     })
 
 fun task29_1(today: MyDate): MyDate {
-    todoTask29()
-//    return today + YEAR + WEEK
+//    todoTask29()
+    return today + YEAR + WEEK
 }
 
 fun task29_2(today: MyDate): MyDate {
-    todoTask29()
-//    return today + YEAR * 2 + WEEK * 3 + DAY * 5
+//    todoTask29()
+    return today + YEAR * 2 + WEEK * 3 + DAY * 5
 }
 
diff --git a/src/iii_conventions/n30DestructuringDeclarations.kt b/src/iii_conventions/n30DestructuringDeclarations.kt
index ed5b757bb..b3811bcb6 100644
--- a/src/iii_conventions/n30DestructuringDeclarations.kt
+++ b/src/iii_conventions/n30DestructuringDeclarations.kt
@@ -11,14 +11,14 @@ fun todoTask30(): Nothing = TODO(
     documentation = doc30()
 )
 
-class MyDate(val year: Int, val month: Int, val dayOfMonth: Int)
+data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int)
 
 fun isLeapDay(date: MyDate): Boolean {
-    todoTask30()
-//    val (year, month, dayOfMonth) = date
-//
-//    // 29 February of a leap year
-//    return isLeapYear(year) && month == 1 && dayOfMonth == 29
+//    todoTask30()
+    val (year, month, dayOfMonth) = date
+
+    // 29 February of a leap year
+    return isLeapYear(year) && month == 1 && dayOfMonth == 29
 }
 
 // Years which are multiples of four (with the exception of years divisible by 100 but not by 400)
diff --git a/src/iii_conventions/n31Invoke.kt b/src/iii_conventions/n31Invoke.kt
index 7feb8a21e..51ea4f5ef 100644
--- a/src/iii_conventions/n31Invoke.kt
+++ b/src/iii_conventions/n31Invoke.kt
@@ -3,7 +3,15 @@ package iii_conventions
 import util.TODO
 
 
-class Invokable
+class Invokable(private var invocations: Int = 0) {
+    operator fun invoke(): Invokable {
+        invocations++
+        return this
+    }
+
+    fun getNumberOfInvocations() = invocations
+}
+
 
 fun todoTask31(): Nothing = TODO(
     """
@@ -14,6 +22,6 @@ fun todoTask31(): Nothing = TODO(
     references = { invokable: Invokable -> })
 
 fun task31(invokable: Invokable): Int {
-    todoTask31()
-//    return invokable()()()().getNumberOfInvocations()
+//    todoTask31()
+    return invokable()()()().getNumberOfInvocations()
 }
diff --git a/src/iv_properties/n32Properties.kt b/src/iv_properties/n32Properties.kt
index 3f2b51f37..fb04eba27 100644
--- a/src/iv_properties/n32Properties.kt
+++ b/src/iv_properties/n32Properties.kt
@@ -5,7 +5,12 @@ import util.doc32
 
 class PropertyExample() {
     var counter = 0
-    var propertyWithCounter: Int? = todoTask32()
+    var propertyWithCounter: Int? = null
+        set(v) {
+            field = v
+            counter++
+        }
+
 }
 
 fun todoTask32(): Nothing = TODO(
diff --git a/src/iv_properties/n33LazyProperty.kt b/src/iv_properties/n33LazyProperty.kt
index 2da09cb24..cc9c12198 100644
--- a/src/iv_properties/n33LazyProperty.kt
+++ b/src/iv_properties/n33LazyProperty.kt
@@ -3,7 +3,16 @@ package iv_properties
 import util.TODO
 
 class LazyProperty(val initializer: () -> Int) {
-    val lazy: Int = todoTask33()
+    private var lazyValue: Int? = null
+        get() {
+            if (field == null) field = initializer()
+            return field
+        }
+    val lazy: Int
+        get() = lazyValue!!
+
+
+
 }
 
 fun todoTask33(): Nothing = TODO(
diff --git a/src/iv_properties/n34DelegatesExamples.kt b/src/iv_properties/n34DelegatesExamples.kt
index 11ad7d481..c306b8374 100644
--- a/src/iv_properties/n34DelegatesExamples.kt
+++ b/src/iv_properties/n34DelegatesExamples.kt
@@ -4,7 +4,7 @@ import util.TODO
 import util.doc34
 
 class LazyPropertyUsingDelegates(val initializer: () -> Int) {
-    val lazyValue: Int by todoTask34()
+    val lazyValue: Int by lazy(initializer)
 }
 
 fun todoTask34(): Lazy<Int> = TODO(
diff --git a/src/iv_properties/n35HowDelegatesWork.kt b/src/iv_properties/n35HowDelegatesWork.kt
index 0462f5556..2f4ff4de4 100644
--- a/src/iv_properties/n35HowDelegatesWork.kt
+++ b/src/iv_properties/n35HowDelegatesWork.kt
@@ -29,8 +29,8 @@ class D {
 class EffectiveDate<R> : ReadWriteProperty<R, MyDate> {
     var timeInMillis: Long? = null
 
-    operator override fun getValue(thisRef: R, property: KProperty<*>): MyDate = todoTask35()
-    operator override fun setValue(thisRef: R, property: KProperty<*>, value: MyDate) = todoTask35()
+    operator override fun getValue(thisRef: R, property: KProperty<*>): MyDate = timeInMillis!!.toDate()
+    operator override fun setValue(thisRef: R, property: KProperty<*>, value: MyDate) { timeInMillis = value.toMillis() }
 }
 
 fun MyDate.toMillis(): Long {
diff --git a/src/v_builders/n36ExtensionFunctionLiterals.kt b/src/v_builders/n36ExtensionFunctionLiterals.kt
index 066c44a26..b1ea35e37 100644
--- a/src/v_builders/n36ExtensionFunctionLiterals.kt
+++ b/src/v_builders/n36ExtensionFunctionLiterals.kt
@@ -14,8 +14,8 @@ fun todoTask36(): Nothing = TODO(
 )
 
 fun task36(): List<Boolean> {
-    val isEven: Int.() -> Boolean = { todoTask36() }
-    val isOdd: Int.() -> Boolean = { todoTask36() }
+    val isEven: Int.() -> Boolean = { this % 2 == 0 }
+    val isOdd: Int.() -> Boolean = { !isEven() }
 
     return listOf(42.isOdd(), 239.isOdd(), 294823098.isEven())
 }
diff --git a/src/v_builders/n37StringAndMapBuilders.kt b/src/v_builders/n37StringAndMapBuilders.kt
index 76e554f5a..96b0b8ba9 100644
--- a/src/v_builders/n37StringAndMapBuilders.kt
+++ b/src/v_builders/n37StringAndMapBuilders.kt
@@ -27,12 +27,18 @@ fun todoTask37(): Nothing = TODO(
     """
 )
 
+fun <K, V> buildMap(build: MutableMap<K, V>.() -> Unit): Map<K, V> {
+    val map = HashMap<K, V>()
+    map.build()
+    return map
+}
+
 fun task37(): Map<Int, String> {
-    todoTask37()
-//    return buildMap {
-//        put(0, "0")
-//        for (i in 1..10) {
-//            put(i, "$i")
-//        }
-//    }
+//    todoTask37()
+    return buildMap {
+        put(0, "0")
+        for (i in 1..10) {
+            put(i, "$i")
+        }
+    }
 }
diff --git a/src/v_builders/n38TheFunctionApply.kt b/src/v_builders/n38TheFunctionApply.kt
index 61a677850..90686b3e4 100644
--- a/src/v_builders/n38TheFunctionApply.kt
+++ b/src/v_builders/n38TheFunctionApply.kt
@@ -9,7 +9,8 @@ fun todoTask38(): Nothing = TODO(
 )
 
 fun <T> T.myApply(f: T.() -> Unit): T {
-    todoTask38()
+    f()
+    return this
 }
 
 fun buildString(): String {
diff --git a/src/v_builders/n39HtmlBuilders.kt b/src/v_builders/n39HtmlBuilders.kt
index 578d50521..0547e75d9 100644
--- a/src/v_builders/n39HtmlBuilders.kt
+++ b/src/v_builders/n39HtmlBuilders.kt
@@ -22,7 +22,7 @@ fun todoTask39(): Nothing = TODO(
 fun renderProductTable(): String {
     return html {
         table {
-            tr {
+            tr (color = getTitleColor()) {
                 td {
                     text("Product")
                 }
@@ -34,7 +34,20 @@ fun renderProductTable(): String {
                 }
             }
             val products = getProducts()
-            todoTask39()
+//            todoTask39()
+            for ((index, product) in products.withIndex()) {
+                tr {
+                    td (color = getCellColor(index, 0)) {
+                        text(product.description)
+                    }
+                    td (color = getCellColor(index, 1)) {
+                        text(product.price)
+                    }
+                    td (color = getCellColor(index, 2)) {
+                        text(product.popularity)
+                    }
+                }
+            }
         }
     }.toString()
 }
diff --git a/src/v_builders/n40BuildersHowItWorks.kt b/src/v_builders/n40BuildersHowItWorks.kt
index 95a8a705e..023ed20bf 100644
--- a/src/v_builders/n40BuildersHowItWorks.kt
+++ b/src/v_builders/n40BuildersHowItWorks.kt
@@ -32,7 +32,7 @@ fun task40() = linkedMapOf<Int, Answer>(
     b. function declaration
     c. function invocation
  */
-    1 to insertAnswerHere(),
+    1 to c,
 
 /*
 2. In the Kotlin code
@@ -49,7 +49,7 @@ fun task40() = linkedMapOf<Int, Answer>(
   b. argument name
   c. argument value
  */
-    2 to insertAnswerHere(),
+    2 to b,
 
 /*
 3. The block
@@ -62,7 +62,7 @@ from the previous question is:
   c. something mysterious
 
  */
-    3 to insertAnswerHere(),
+    3 to b,
 
 /*
 4. For the code
@@ -84,5 +84,5 @@ which of the following is true:
                   }
             }
  */
-    4 to insertAnswerHere()
+    4 to c
 )
diff --git a/src/vi_generics/n41GenericFunctions.kt b/src/vi_generics/n41GenericFunctions.kt
index 38d333c9c..f12bdc66b 100644
--- a/src/vi_generics/n41GenericFunctions.kt
+++ b/src/vi_generics/n41GenericFunctions.kt
@@ -19,12 +19,23 @@ fun task41(): Nothing = TODO(
     }
 )
 
+fun <T, C: MutableCollection<T>> Collection<T>.partitionTo(first: C, second: C, predicate: (T) -> Boolean): Pair<C, C> {
+    for (element in this) {
+        if (predicate(element)) {
+            first.add(element)
+        } else {
+            second.add(element)
+        }
+    }
+    return Pair(first, second)
+}
+
 fun List<String>.partitionWordsAndLines(): Pair<List<String>, List<String>> {
-    task41()
-//    return partitionTo(ArrayList<String>(), ArrayList()) { s -> !s.contains(" ") }
+//    task41()
+    return partitionTo(ArrayList<String>(), ArrayList()) { s -> !s.contains(" ") }
 }
 
 fun Set<Char>.partitionLettersAndOtherSymbols(): Pair<Set<Char>, Set<Char>> {
-    task41()
-//    return partitionTo(HashSet<Char>(), HashSet()) { c -> c in 'a'..'z' || c in 'A'..'Z'}
+//    task41()
+    return partitionTo(HashSet<Char>(), HashSet()) { c -> c in 'a'..'z' || c in 'A'..'Z'}
 }
\ No newline at end of file