diff --git a/13.1.py b/13.1.py
new file mode 100644
index 0000000..7909980
--- /dev/null
+++ b/13.1.py
@@ -0,0 +1,102 @@
+class Person: #Клас Особа
+    def __init__(self, name = '', surname = '', age = 0):
+        self.name = name
+        self.surname = surname
+        self.age = age
+
+    def __str__(self):
+        return f'{self.name} {self.surname}, {self.age}'
+
+    def input(self):
+        self.name = input('Enter name: ')
+        self.surname = input('Enter surname: ')
+        self.age = int(input('Enter age: '))
+
+    def __repr__(self):
+        return f'Person({self.name}, {self.surname}, {self.age})'
+
+class Acquainted(Person):
+    def __init__(self, name = '', surname = '', age = 0, phone_numb = ''):
+        self.name = name
+        self.surname = surname
+        self.age = age
+        self.phone_numb = phone_numb
+
+    def __str__(self):
+        return f'{self.name} {self.surname} {self.age} {self.phone_numb}'
+
+    def inp_phone(self):
+        self.phone_numb = input('Enter phone number: ')
+
+    def set_phone(self, phone_numb):
+        self.phone_numb = phone_numb
+
+    def get_phone(self):
+        return self.phone_numb
+
+class Notebook:
+    def __init__(self, fname):
+        self.lst = []
+        self.fname = fname
+        try:
+            f = open(fname)
+            for line in f.readlines():
+                s1 = line.split()[0]
+                s2 = line.split()[1]
+                s3 = int(line.split()[2])
+                s4 = line.split()[3]
+                acq = Acquainted(s1, s2, s3, s4)
+                self.lst.append(acq)
+            f.close()
+        except:
+            print('Bad file')
+
+    def upd(self, a = None):
+        if a is None:
+            a = Acquainted()
+            a.input()
+            a.inp_phone()
+        self.lst.append(a)
+        f = open(self.fname, 'w+')
+        for x in self.lst:
+            f.write(' '.join([x.name, x.surname, str(x.age), x.phone_numb]))
+            f.write('\n')
+        f.close()
+
+    def upd2(self):
+        n = int(input('Number of acquaintance: '))
+        for _ in range(n):
+            self.upd()
+        f = open(self.fname, 'w+')
+        for x in self.lst:
+            f.write(' '.join([x.name, x.surname, str(x.age), x.phone_numb]))
+            f.write('\n')
+        f.close()
+
+    def __str__(self):
+        return '\n'.join(str(x) for x in self.lst)
+
+    def finder(self, surname):
+        for item in self.lst:
+            if item.surname == surname:
+                return item.get_phone()
+        return None
+
+    def changer(self, surname, new_phone):
+        for item in self.lst:
+            if item.surname == surname:
+                item.set_phone(new_phone)
+                return True
+        return None
+
+
+if __name__ == "__main__":
+    p = Person()
+    p.input()
+    print(p)
+    print(repr(p))
+    a = Acquainted()
+    a.input()
+    a.inp_phone()
+    print(a)
+
diff --git a/13.7.py b/13.7.py
new file mode 100644
index 0000000..f300794
--- /dev/null
+++ b/13.7.py
@@ -0,0 +1,68 @@
+class Segment:
+
+    def __init__(self, a, b):
+        assert a <= b, 'b > a'
+        self.a = a
+        self.b = b
+
+        if self.a == self.b:
+            self.empty = True
+        else:
+            self.empty = False
+        
+        self.seg = (self.a, self.b, self.empty)
+
+    def __str__(self):
+        return f'({self.a}, {self.b}, {self.empty})'
+
+    def make_empty(self):
+        self.a = self.b = 0
+        self.empty = True
+
+    def is_empty(self):
+        return self.empty
+    
+    def intersect(self, t):
+        if self.empty or t.empty:
+            return self.make_empty()
+
+        if self.b < t.a or self.a > t.b:
+            return self.make_empty()
+
+        if self.a >= t.a and self.b <= t.b:
+            return self
+        elif self.a <= t.a and self.b >= t.b:
+            return t
+        
+        if self.a >= t.a and self.b >= t.b:
+            return Segment(self.a, t.b)
+        elif self.a <= t.a and self.b <= t.b:
+            return Segment(t.a, self.b)
+    
+
+
+    
+
+if __name__ == "__main__":
+    # t1 = Segment(-1, 3)
+    # t2 = Segment(0, 9)
+    # t = t1.intersect(t2)
+    # print(t)
+
+    p = int(input('p = '))
+    q = int(input('q = '))
+    d = p**2 - 4*q
+    x_1 = (-p - d**0.5)/2
+    x_2 = (-p + d**0.5)/2
+    t_1 = Segment(x_1, x_2)
+
+    p = int(input('p = '))
+    q = int(input('q = '))
+    d = p**2 - 4*q
+    x_1 = (-p - d**0.5)/2
+    x_2 = (-p + d**0.5)/2
+    t_2 = Segment(x_1, x_2)
+
+    print(t_1.intersect(t_2))
+
+
diff --git a/13.8.py b/13.8.py
new file mode 100644
index 0000000..828192a
--- /dev/null
+++ b/13.8.py
@@ -0,0 +1,80 @@
+class MultiSet:
+
+    def __init__(self):
+
+        self.dct = {}
+
+    def makeEmpty(self):
+        self.dct.clear()
+
+    def isEmpty(self):
+        return not bool(self.dct)
+
+    def addElement(self, el):
+        self.dct[el] = self.dct.get(el, 0) + 1
+
+    def popElement(self, el):
+        self.dct[el] = self.dct.get(el, 0) - 1
+        if self.dct[el] <= 0:
+            del self.dct[el]
+
+    def countElement(self, el):
+        return self.dct.get(el, 0)
+
+    def union(self, ms):
+        
+        keys1 = set(self.dct.keys())
+        keys2 = set(ms.dct.keys())
+
+        keys = keys1 | keys2
+
+        for item in keys:
+            self.dct[item] = max(self.dct.get(item, 0), ms.dct.get(item, 0))
+
+    def intersect(self, ms):
+
+        keys1 = set(self.dct.keys())
+        keys2 = set(ms.dct.keys())
+
+        keys = keys1 & keys2
+
+        rem = keys1 - keys2
+        for item in rem:
+            del self.dct[item]
+
+        for item in keys:
+            self.dct[item] = min(self.dct.get(item, 0), ms.dct.get(item, 0)) 
+
+    def __str__(self):
+        st = "{"
+        for k, v in self.dct.items():
+            st += f"({k}, {v}), "
+        st += "}\n"
+        return st
+
+if __name__ == "__main__":
+
+    m1 = MultiSet()
+    m1.addElement(3)
+    m1.addElement(2)
+    m1.addElement(1)
+    m1.addElement(3)
+    m1.addElement(3)
+    m1.addElement(1)
+    print(m1)
+
+    m2 = MultiSet()
+    m2.addElement(1)
+    m2.addElement(3)
+    m2.addElement(1)
+    m2.addElement(3)
+    m2.addElement(3)
+    m2.addElement(1)
+    print(m2)
+
+    m1.union(m2)
+    print(m1)
+
+    m1.intersect(m2)
+    print(m1)
+