diff --git a/books.dtd b/books.dtd
new file mode 100644
index 0000000..882af16
--- /dev/null
+++ b/books.dtd
@@ -0,0 +1,12 @@
+<!ELEMENT bookstore (book*)>
+<!ELEMENT book (title, year, price, author+)>
+<!ELEMENT title (#PCDATA)>
+<!ELEMENT year (#PCDATA)>
+<!ELEMENT price (#PCDATA)>
+<!ELEMENT author (#PCDATA)>
+
+<!ATTLIST book
+        category CDATA #REQUIRED
+        cover (hardpack | paperpack) "paperback" #IMPLIED>
+<!ATTLIST title
+        lang CDATA #REQUIRED>
\ No newline at end of file
diff --git a/books.xml b/books.xml
index 49f0348..af29485 100644
--- a/books.xml
+++ b/books.xml
@@ -1,4 +1,6 @@
-<bookstore>
+<?xml-stylesheet type="text/xsl" href="task24.xsl"?>
+<bookstore xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+        xsi:noNamespaceSchemaLocation="books.xsd">
   <book category="cooking">
     <title lang="en">Everyday Italian</title>
     <author>Giada De Laurentiis</author>
@@ -21,7 +23,7 @@
     <year>2003</year>
     <price>49.99</price>
   </book>
-  <book category="web" cover="paperback">
+  <book category="web" cover="paperpack">
     <title lang="en">Learning XML</title>
     <author>Erik T. Ray</author>
     <year>2003</year>
diff --git a/books.xsd b/books.xsd
new file mode 100644
index 0000000..1c265f2
--- /dev/null
+++ b/books.xsd
@@ -0,0 +1,71 @@
+<?xml version="1.0"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
+
+    <xs:element name="bookstore" type="bookstore_type"/>
+    <xs:element name="book" type="book_type"/>
+
+    <xs:complexType name="bookstore_type">
+        <xs:sequence>
+            <xs:element ref="book" minOccurs="0" maxOccurs="100"/>
+        </xs:sequence>
+    </xs:complexType>
+
+    <xs:complexType name="book_type">
+        <xs:complexContent>
+            <xs:extension base="book_type_elements">
+                <xs:attribute name="category" type="xs:string" use="required"/>
+                <xs:attribute name="cover" use="optional">
+                    <xs:simpleType>
+                        <xs:restriction>
+                            <xs:enumeration value="hardpack"/>
+                            <xs:enumeration value="paperpack"/>
+                        </xs:restriction>
+                    </xs:simpleType>
+                </xs:attribute>
+            </xs:extension>
+        </xs:complexContent>
+    </xs:complexType>
+
+    <xs:complexType name="book_type_elements">
+        <xs:sequence>
+            <xs:element name="title" block="">
+                <xs:complexType>
+                    <xs:complexContent>
+                        <xs:extension base="title_type">
+                            <xs:attribute name="lang" type="lang_type" use="required"/>
+                        </xs:extension>
+                    </xs:complexContent>
+                </xs:complexType>
+            </xs:element>
+            <xs:element name="author" type="xs:string" minOccurs="1" maxOccurs="100"/>
+            <xs:element name="year">
+                <xs:simpleType>
+                    <xs:restriction base="xs:integer">
+                        <xs:minExclusive value="1900"/>
+                        <xs:maxInclusive value="2014"/>
+                    </xs:restriction>
+                </xs:simpleType>
+            </xs:element>
+            <xs:element name="price">
+                <xs:simpleType>
+                    <xs:restriction base="xs:double">
+                        <xs:minInclusive value="0"/>
+                    </xs:restriction>
+                </xs:simpleType>
+            </xs:element>
+        </xs:sequence>
+    </xs:complexType>
+
+    <xs:simpleType name="lang_type">
+        <xs:restriction>
+            <xs:length value="2"/>
+        </xs:restriction>
+    </xs:simpleType>
+    
+    <xs:simpleType name="title_type">
+        <xs:restriction>
+            <xs:minLength value="2"/>
+            <xs:maxLength value="30"/>
+        </xs:restriction>
+    </xs:simpleType>
+</xs:schema>
\ No newline at end of file
diff --git a/student.dtd b/student.dtd
index 3613239..2de1630 100644
--- a/student.dtd
+++ b/student.dtd
@@ -1 +1,5 @@
 <!ELEMENT student EMPTY>
+<!ATTLIST student 
+	fullname CDATA #REQUIRED
+	group (К6-361|К6-362) #REQUIRED
+>
diff --git a/student.xml b/student.xml
new file mode 100644
index 0000000..c07c6d6
--- /dev/null
+++ b/student.xml
@@ -0,0 +1,3 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE student SYSTEM "student.dtd">
+<student fullname="Ivanov Nikolay Vyacheslavovich" group="К6-361"/>
\ No newline at end of file
diff --git a/task16 b/task16
new file mode 100644
index 0000000..2625f83
--- /dev/null
+++ b/task16
@@ -0,0 +1 @@
+//book
\ No newline at end of file
diff --git a/task17 b/task17
new file mode 100644
index 0000000..9a6397a
--- /dev/null
+++ b/task17
@@ -0,0 +1 @@
+//book[@cover]
\ No newline at end of file
diff --git a/task18 b/task18
new file mode 100644
index 0000000..82d7d89
--- /dev/null
+++ b/task18
@@ -0,0 +1 @@
+//book[./year = 2003]
\ No newline at end of file
diff --git a/task19 b/task19
new file mode 100644
index 0000000..df9a07b
--- /dev/null
+++ b/task19
@@ -0,0 +1 @@
+//book[./year >= 30 and ./year < 40]
\ No newline at end of file
diff --git a/task20.xsl b/task20.xsl
new file mode 100644
index 0000000..bfe9d70
--- /dev/null
+++ b/task20.xsl
@@ -0,0 +1,8 @@
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+    <xsl:template match="/">
+        <xsl:for-each select="//book">
+            <xsl:value-of select="./title/text()"/>
+            <xsl:if test="position() != last()"> , </xsl:if>
+        </xsl:for-each>
+    </xsl:template>
+</xsl:stylesheet>
\ No newline at end of file
diff --git a/task21.xsl b/task21.xsl
new file mode 100644
index 0000000..71fced4
--- /dev/null
+++ b/task21.xsl
@@ -0,0 +1,9 @@
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+    <xsl:template match="/">
+        <xsl:for-each select="//book">
+            <xsl:sort order="ascending" select="./price" data-type="number"/>
+            <xsl:value-of select="./title/text()"/>
+            <xsl:if test="position() != last()"> , </xsl:if>
+        </xsl:for-each>
+    </xsl:template>
+</xsl:stylesheet>
\ No newline at end of file
diff --git a/task22.xsl b/task22.xsl
new file mode 100644
index 0000000..bc96083
--- /dev/null
+++ b/task22.xsl
@@ -0,0 +1,9 @@
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+    <xsl:template match="/">
+        <xsl:for-each select="//book">
+            <xsl:value-of select="./title/text()"/>
+            <xsl:if test="count(./author) &gt; 1">*</xsl:if>
+            <xsl:if test="position() != last()"> , </xsl:if>
+        </xsl:for-each>
+    </xsl:template>
+</xsl:stylesheet>
\ No newline at end of file
diff --git a/task23.xsl b/task23.xsl
new file mode 100644
index 0000000..0795156
--- /dev/null
+++ b/task23.xsl
@@ -0,0 +1,11 @@
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+    <xsl:template match="/">
+        <xsl:for-each select="//book">
+            <xsl:value-of select="./title/text()"/>
+            <xsl:if test="./price &gt; 30">&gt;30</xsl:if>
+            <xsl:if test="./price &lt; 30">&lt;30</xsl:if>
+            <xsl:if test="./price = 30">=30</xsl:if>
+            <xsl:if test="position() != last()"> , </xsl:if>
+        </xsl:for-each>
+    </xsl:template>
+</xsl:stylesheet>
\ No newline at end of file
diff --git a/task24.xsl b/task24.xsl
new file mode 100644
index 0000000..8352529
--- /dev/null
+++ b/task24.xsl
@@ -0,0 +1,28 @@
+<?xml version="1.0"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+    <xsl:output method="xml" indent="yes"/>
+
+    <xsl:template match="/">
+        <library>
+            <xsl:apply-templates/>
+        </library>
+    </xsl:template>
+
+    <xsl:template match="//book">
+        <book>
+            <xsl:attribute name="title">
+                <xsl:value-of select="./title"/>
+            </xsl:attribute>
+            <xsl:attribute name="year">
+                <xsl:value-of select="./year"/>
+            </xsl:attribute>
+            <xsl:for-each select="./author">
+                <author>
+                    <xsl:attribute name="name">
+                        <xsl:value-of select="."/>
+                    </xsl:attribute>
+                </author>
+            </xsl:for-each>
+        </book>
+    </xsl:template>
+</xsl:stylesheet>
\ No newline at end of file