diff --git a/books.dtd b/books.dtd
new file mode 100644
index 0000000..acc0bcf
--- /dev/null
+++ b/books.dtd
@@ -0,0 +1,9 @@
+<!DOCTYPE bookstore [
+<!ELEMENT bookstore (book*)>
+<!ELEMENT book (title,year,price,author+)>
+<!ATTLIST book category CDATA #REQUIRED>
+<!ATTLIST book cover CDATA #IMPLIED>
+<!ATTLIST book cover (hardback|paperback)>
+<!ATTLIST title lang CDATA #REQUIRED>
+<!ATTLIST title lang CDATA "en">
+]>
diff --git a/books.xml b/books.xml
index 49f0348..8a8c5dc 100644
--- a/books.xml
+++ b/books.xml
@@ -1,3 +1,13 @@
+<!DOCTYPE bookstore [
+<!ELEMENT bookstore (book*)>
+<!ELEMENT book (title,author+,year,price)>
+<!ATTLIST book category CDATA #REQUIRED>
+<!ATTLIST book cover CDATA #IMPLIED>
+<!ATTLIST book cover (hardback|paperback)>
+<!ATTLIST title lang CDATA #REQUIRED>
+<!ATTLIST title lang CDATA "en">
+]>
+
 <bookstore>
   <book category="cooking">
     <title lang="en">Everyday Italian</title>
diff --git a/books.xsd b/books.xsd
new file mode 100644
index 0000000..64a41f2
--- /dev/null
+++ b/books.xsd
@@ -0,0 +1,77 @@
+<?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..f676f88 100644
--- a/student.dtd
+++ b/student.dtd
@@ -1 +1,4 @@
-<!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..e74f7ad
--- /dev/null
+++ b/student.xml
@@ -0,0 +1,3 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE student SYSTEM "student.dtd">
+<student fullname="Сашин Александр Андреевич" group="К6-362" />
diff --git a/task16 b/task16
new file mode 100644
index 0000000..52639a1
--- /dev/null
+++ b/task16
@@ -0,0 +1 @@
+//book
diff --git a/task17 b/task17
new file mode 100644
index 0000000..f582071
--- /dev/null
+++ b/task17
@@ -0,0 +1 @@
+//book[@cover]
diff --git a/task18 b/task18
new file mode 100644
index 0000000..ed203f4
--- /dev/null
+++ b/task18
@@ -0,0 +1 @@
+//book[child::year=2003]
diff --git a/task19 b/task19
new file mode 100644
index 0000000..172e6bf
--- /dev/null
+++ b/task19
@@ -0,0 +1 @@
+//book[child::price >= 30 and child::price < 40
diff --git a/task20.xsl b/task20.xsl
new file mode 100644
index 0000000..b21919d
--- /dev/null
+++ b/task20.xsl
@@ -0,0 +1,15 @@
+<?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>&#xA0;</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..4f0fda0
--- /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>&#xA0;</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..695d016
--- /dev/null
+++ b/task22.xsl
@@ -0,0 +1,19 @@
+<?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>&#xA0;</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..ee319c9
--- /dev/null
+++ b/task23.xsl
@@ -0,0 +1,31 @@
+<?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>&#xA0;</xsl:text>
+    </xsl:for-each>
+  </body>
+</html>
+
+</xsl:template>
+</xsl:stylesheet>