diff --git a/books.dtd b/books.dtd
new file mode 100644
index 0000000..4e1e435
--- /dev/null
+++ b/books.dtd
@@ -0,0 +1,12 @@
+<!ELEMENT bookstore (book*)>
+<!ELEMENT book (title, author+, year, price)>
+<!ATTLIST book category CDATA #REQUIRED
+	cover (hardback|paperback) #IMPLIED
+>
+<!ELEMENT title (#PCDATA)>
+<!ATTLIST title
+	lang CDATA "en"
+>
+<!ELEMENT author (#PCDATA)>
+<!ELEMENT year (#PCDATA)>
+<!ELEMENT price (#PCDATA)>
diff --git a/books.xml b/books.xml
index 49f0348..5b51289 100644
--- a/books.xml
+++ b/books.xml
@@ -1,3 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE bookstore SYSTEM "books.dtd">
 <bookstore>
   <book category="cooking">
     <title lang="en">Everyday Italian</title>
diff --git a/books.xsd b/books.xsd
new file mode 100644
index 0000000..49cbab4
--- /dev/null
+++ b/books.xsd
@@ -0,0 +1,68 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
+	<xs:element name="bookstore" type="bookstoreType"/>
+	<xs:complexType name="bookstoreType">
+		<xs:sequence>
+			<xs:element name="book" type="bookType" minOccurs="0" maxOccurs="unbounded"/>
+		</xs:sequence>
+	</xs:complexType>
+	<xs:complexType name="bookType">
+		<xs:sequence>
+			<xs:element name="title">
+				<xs:complexType>
+					<xs:simpleContent>
+						<xs:restriction base="titleType">
+							<xs:minLength value="2"/>
+							<xs:maxLength value="30"/>
+						</xs:restriction>
+					</xs:simpleContent>
+				</xs:complexType>
+			</xs:element>
+			<xs:element name="author" minOccurs="1" maxOccurs="unbounded">
+				<xs:simpleType>
+					<xs:restriction base="xs:string">
+						<xs:minLength value="2"/>
+						<xs:maxLength value="30"/>
+					</xs:restriction>
+				</xs:simpleType>
+			</xs:element>
+			<xs:element name="year">
+				<xs:simpleType>
+					<xs:restriction base="xs:integer">
+						<xs:minInclusive value="1900"/>
+						<xs:maxInclusive value="2014"/>
+					</xs:restriction>
+				</xs:simpleType>
+			</xs:element>
+			<xs:element name="price">
+				<xs:simpleType>
+					<xs:restriction base="xs:decimal">
+						<xs:minInclusive value="0"/>
+					</xs:restriction>
+				</xs:simpleType>
+			</xs:element>
+		</xs:sequence>
+		<xs:attribute name="category" type="xs:string" use="required"/>
+		<xs:attribute name="cover" use="optional">
+			<xs:simpleType>
+				<xs:restriction base="xs:string">
+					<xs:enumeration value="hardback"/>
+					<xs:enumeration value="paperback"/>
+				</xs:restriction>
+			</xs:simpleType>
+		</xs:attribute>
+	</xs:complexType>
+	<xs:complexType name="titleType">
+		<xs:simpleContent>
+			<xs:extension base="xs:string">
+				<xs:attribute name="lang" use="required">
+					<xs:simpleType>
+						<xs:restriction base="xs:string">
+							<xs:length value="2"/>
+						</xs:restriction>
+					</xs:simpleType>
+				</xs:attribute>
+			</xs:extension>
+		</xs:simpleContent>
+	</xs:complexType>
+</xs:schema>
diff --git a/student.dtd b/student.dtd
index 3613239..16477a9 100644
--- a/student.dtd
+++ b/student.dtd
@@ -1 +1,5 @@
-<!ELEMENT student EMPTY>
+<!ELEMENT student ANY>
+<!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..bd706af
--- /dev/null
+++ b/student.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE student SYSTEM "student.dtd">
+<student fullname = "Chaikovskaia Aleksandra" group = "К6-362">
+</student>
diff --git a/task16 b/task16
new file mode 100644
index 0000000..c374ff8
--- /dev/null
+++ b/task16
@@ -0,0 +1 @@
+"/bookstore/book"
diff --git a/task17 b/task17
new file mode 100644
index 0000000..c2379cd
--- /dev/null
+++ b/task17
@@ -0,0 +1 @@
+"/bookstore/book[@cover]"
diff --git a/task18 b/task18
new file mode 100644
index 0000000..c3a2da2
--- /dev/null
+++ b/task18
@@ -0,0 +1 @@
+"/bookstore/book[@year=2003]"
diff --git a/task19 b/task19
new file mode 100644
index 0000000..1e1b4f5
--- /dev/null
+++ b/task19
@@ -0,0 +1 @@
+"/bookstore/book[@price>=30 and @price<40]"
diff --git a/task20.xsl b/task20.xsl
new file mode 100644
index 0000000..1096d82
--- /dev/null
+++ b/task20.xsl
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+	<xsl:output method="text"/>
+	<xsl:template match="/">
+		<html>
+			<body>
+				<xsl:for-each select="//book">
+					<xsl:value-of select="title"/> <xsl:text>&#xa;</xsl:text>
+				</xsl:for-each>
+			</body>
+		</html>
+	</xsl:template>
+</xsl:stylesheet>
+
diff --git a/task21.xsl b/task21.xsl
new file mode 100644
index 0000000..a36d920
--- /dev/null
+++ b/task21.xsl
@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+	<xsl:output method="text"/>
+	<xsl:template match="/">
+		<html>
+			<body>
+				<xsl:for-each select="//book">
+					<xsl:sort select="price"/>
+					<xsl:value-of select="title"/> 
+					<xsl:text>&#xa;</xsl:text>
+				</xsl:for-each>
+			</body>
+		</html>
+	</xsl:template>
+</xsl:stylesheet>
+
diff --git a/task22.xsl b/task22.xsl
new file mode 100644
index 0000000..a24f143
--- /dev/null
+++ b/task22.xsl
@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+	<xsl:output method="text"/>
+	<xsl:template match="/">
+		<html>
+			<body>
+				<xsl:for-each select="//book">
+					<xsl:value-of select="title"/>
+					<xsl:if test="count(author) &gt; 1">
+						<xsl:text>*</xsl:text>
+					</xsl:if>
+					<xsl:text>&#xa;</xsl:text>
+				</xsl:for-each>
+			</body>
+		</html>
+	</xsl:template>
+</xsl:stylesheet>
+
diff --git a/task23.xsl b/task23.xsl
new file mode 100644
index 0000000..ff7eb10
--- /dev/null
+++ b/task23.xsl
@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+	<xsl:output method="text"/>
+	<xsl:template match="/">
+		<html>
+			<body>
+				<xsl:for-each select="//book">
+					<xsl:value-of select="title"/>
+					<xsl:choose>
+						<xsl:when test="price &gt; 30">
+							<xsl:text>&gt;30</xsl:text>
+						</xsl:when>
+						<xsl:otherwise>
+							<xsl:choose>
+								<xsl:when test="price &lt; 30">
+									<xsl:text>&lt;30</xsl:text>
+								</xsl:when>
+								<xsl:otherwise>
+									<xsl:text>=30</xsl:text>
+								</xsl:otherwise>
+							</xsl:choose>
+						</xsl:otherwise>
+					</xsl:choose>
+					<xsl:text>&#xa;</xsl:text>
+				</xsl:for-each>
+			</body>
+		</html>
+	</xsl:template>
+</xsl:stylesheet>
diff --git a/task24.xsl b/task24.xsl
new file mode 100644
index 0000000..9738cdb
--- /dev/null
+++ b/task24.xsl
@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+	<xsl:output method="text"/>
+	<xsl:template match="/">
+		<html>
+			<body>
+				<xsl:text>&lt;?xml version="1.0" encoding="UTF-8"?&gt;&#xa;&lt;library&gt;</xsl:text>
+				<xsl:apply-templates/>
+				<xsl:text>&lt;/library&gt;</xsl:text>
+			</body>
+		</html>
+	</xsl:template>
+	<xsl:template match="book">
+		<xsl:text>&lt;book title="</xsl:text>
+		<xsl:value-of select="title"/>
+		<xsl:text>" year="</xsl:text>
+		<xsl:value-of select="year"/>
+		<xsl:text>"&gt;</xsl:text>
+		<xsl:apply-templates select="author"/>
+		<xsl:text>&lt;/book&gt;</xsl:text>
+	</xsl:template>
+	<xsl:template match="author">
+		<xsl:text>&lt;author name="</xsl:text>
+		<xsl:value-of select="."/>
+		<xsl:text>"&gt;</xsl:text>
+		<xsl:text>&lt;/author&gt;</xsl:text>
+	</xsl:template>
+</xsl:stylesheet>