diff --git a/src/codewars/SimpleWebFramework.py b/src/codewars/SimpleWebFramework.py
index dd111de..50ceb7a 100644
--- a/src/codewars/SimpleWebFramework.py
+++ b/src/codewars/SimpleWebFramework.py
@@ -2,7 +2,6 @@ import typing
 
 
 class Router(object):
-
     def __init__(self):
         self.routes = {}
 
diff --git a/src/codewars/chemist.py b/src/codewars/chemist.py
new file mode 100644
index 0000000..28383b7
--- /dev/null
+++ b/src/codewars/chemist.py
@@ -0,0 +1,303 @@
+PERIODIC_TABLE: dict[str, tuple[int, float | int]] = {
+    "H": (1, 1.0),
+    "B": (3, 10.8),
+    "C": (4, 12.0),
+    "N": (3, 14.0),
+    "O": (2, 16.0),
+    "F": (1, 19.0),
+    "Mg": (2, 24.3),
+    "P": (3, 31.0),
+    "S": (2, 32.1),
+    "Cl": (1, 35.5),
+    "Br": (1, 80.0),
+}
+
+
+class LockedMolecule(Exception):
+    pass
+
+
+class UnlockedMolecule(Exception):
+    pass
+
+
+class InvalidBond(Exception):
+    pass
+
+
+class EmptyMolecule(Exception):
+    pass
+
+
+class Atom(object):
+    def __init__(self, elt: str, id_: int):
+        self.element = elt
+        self.id = id_
+        self.bounds = []
+        self.max_bounds = PERIODIC_TABLE[self.element][0]
+        self.weight = PERIODIC_TABLE[self.element][1]
+
+    def __hash__(self):
+        return self.id
+
+    def __eq__(self, other):
+        return self.id == other.id
+
+    def __str__(self):
+        bounds = []
+
+        bounds.extend(
+            list(sorted(Molecule.filter_element(self.bounds, "C"), key=lambda b: b.id))
+        )
+        bounds.extend(
+            list(sorted(Molecule.filter_element(self.bounds, "O"), key=lambda b: b.id))
+        )
+
+        for bound in list(
+            sorted(sorted(self.bounds, key=lambda b: b.id), key=lambda b: b.element)
+        ):
+            if bound.element not in ["C", "H", "O"]:
+                bounds.append(bound)
+
+        bounds.extend(
+            list(sorted(Molecule.filter_element(self.bounds, "H"), key=lambda b: b.id))
+        )
+
+        return (
+            f"Atom({self.element}.{self.id}"
+            f"{': ' if bounds else ''}"
+            f"{','.join(bound.element + (str(bound.id) if bound.element != 'H' else '') for bound in bounds)})"
+        )
+
+    def add_bound(self, atom):
+        if self == atom:
+            raise InvalidBond
+        if len(self.bounds) >= self.max_bounds:
+            raise InvalidBond
+
+        self.bounds.append(atom)
+
+    @staticmethod
+    def remove_bounds(atom1, atom2):
+        if not (atom1 or atom2):
+            return
+
+        if atom1 in atom2.bounds:
+            atom2.bounds.remove(atom1)
+
+        if atom2 in atom1.bounds:
+            atom1.bounds.remove(atom2)
+
+    def mutate(self, element: str):
+        if len(self.bounds) > PERIODIC_TABLE[element][0]:
+            raise InvalidBond
+
+        self.element = element
+        self.max_bounds = PERIODIC_TABLE[self.element][0]
+        self.weight = PERIODIC_TABLE[self.element][1]
+
+    def unlock(self):
+        self.bounds = list(filter(lambda atom: atom.element != "H", self.bounds))
+
+
+class Molecule(object):
+    name: str
+    _formula: str
+    _molecular_weight: float
+    atoms: list[Atom]
+    branches: dict[int, list[Atom]]
+    locked: bool = False
+    exception_thrown = False
+
+    def __init__(self, name=""):
+        self.name = name
+        self.atoms = []
+        self.branches = {}
+
+    @staticmethod
+    def filter_element(atoms: list[Atom], element: str) -> list[Atom]:
+        return list(filter(lambda atom: element == atom.element, atoms))
+
+    def brancher(self, *branches: int):
+        if self.locked:
+            raise LockedMolecule
+
+        for carbons in branches:
+            branch_id = len(self.branches) + 1
+            self.branches[branch_id] = []
+            for i in range(1, carbons + 1):
+                atom = Atom(elt="C", id_=len(self.atoms) + i)
+                self.branches[branch_id].append(atom)
+
+                if i > 1:
+                    last_atom = self.branches[branch_id][i - 2]
+
+                    try:
+                        atom.add_bound(last_atom)
+                        last_atom.add_bound(atom)
+                    except InvalidBond as e:
+                        Atom.remove_bounds(atom, last_atom)
+                        raise e
+
+            self.atoms.extend(self.branches[branch_id])
+        return self
+
+    def bounder(self, *bounds: tuple[int, int, int, int]):
+        if self.locked:
+            raise LockedMolecule
+
+        for c1, b1, c2, b2 in bounds:
+            atom1 = self.branches[b1][c1 - 1]
+            atom2 = self.branches[b2][c2 - 1]
+
+            atom1_bounds = atom1.bounds[:]
+            atom2_bounds = atom2.bounds[:]
+
+            try:
+                atom1.add_bound(atom2)
+                atom2.add_bound(atom1)
+            except InvalidBond as e:
+                atom1.bounds = atom1_bounds
+                atom2.bounds = atom2_bounds
+                raise e
+
+        return self
+
+    def mutate(self, *mutations: tuple[int, int, str]):
+        if self.locked:
+            raise LockedMolecule
+
+        for nc, nb, element in mutations:
+            atom = self.branches[nb][nc - 1]
+            try:
+                atom.mutate(element)
+            except InvalidBond as e:
+                raise e
+
+        return self
+
+    def add(self, *additions: tuple[int, int, str]):
+        if self.locked:
+            raise LockedMolecule
+
+        for nc, nb, element in additions:
+            atom = Atom(elt=element, id_=len(self.atoms) + 1)
+            carbon = self.branches[nb][nc - 1]
+
+            try:
+                carbon.add_bound(atom)
+                atom.add_bound(carbon)
+            except InvalidBond as e:
+                Atom.remove_bounds(carbon, atom)
+                raise e
+
+            self.atoms.append(atom)
+
+        return self
+
+    def add_chaining(self, nc: int, nb: int, *elements: str):
+        if self.locked:
+            raise LockedMolecule
+
+        carbon = self.branches[nb][nc - 1]
+
+        chain = []
+
+        try:
+            last_atom = Atom(elt=elements[0], id_=len(self.atoms) + len(chain) + 1)
+            chain.append(last_atom)
+
+            for element in elements[1:]:
+                atom = Atom(elt=element, id_=len(self.atoms) + len(chain) + 1)
+                chain.append(atom)
+                last_atom.add_bound(atom)
+                atom.add_bound(last_atom)
+                last_atom = atom
+        except InvalidBond as e:
+            Atom.remove_bounds(atom, last_atom)
+            raise e
+
+        try:
+            carbon.add_bound(chain[0])
+            chain[0].add_bound(carbon)
+        except InvalidBond as e:
+            Atom.remove_bounds(carbon, chain[0])
+            raise e
+
+        self.atoms.extend(chain)
+
+        return self
+
+    def closer(self):
+        if self.locked:
+            raise LockedMolecule
+
+        try:
+            for atom in self.atoms:
+                while len(atom.bounds) < atom.max_bounds:
+                    hydrogen = Atom(elt="H", id_=len(self.atoms) + 1)
+                    atom.add_bound(hydrogen)
+                    hydrogen.add_bound(atom)
+                    self.atoms.append(hydrogen)
+        except InvalidBond as e:
+            Atom.remove_bounds(atom, hydrogen)
+            raise e
+
+        self.locked = True
+
+        return self
+
+    def unlock(self):
+        self.locked = False
+        self.atoms = list(filter(lambda atom: atom.element != "H", self.atoms))
+
+        for new_id, atom in enumerate(self.atoms, start=1):
+            atom.unlock()
+            atom.id = new_id
+
+        new_branches = {}
+        new_id = 1
+        for atoms in self.branches.values():
+            filtered = list(filter(lambda atom: atom.element != "H", atoms))
+            if len(filtered) > 0:
+                new_branches[new_id] = filtered
+                new_id += 1
+
+        self.branches = new_branches
+
+        if not self.branches:
+            raise EmptyMolecule
+
+        return self
+
+    @property
+    def formula(self) -> str:
+        if not self.locked:
+            raise UnlockedMolecule
+
+        elements = set(atom.element for atom in self.atoms)
+        formula = ""
+
+        if "C" in elements:
+            c_len = len(Molecule.filter_element(self.atoms, "C"))
+            formula += f"C{c_len if c_len > 1 else ''}"
+        if "H" in elements:
+            h_len = len(Molecule.filter_element(self.atoms, "H"))
+            formula += f"H{h_len if h_len > 1 else ''}"
+        if "O" in elements:
+            o_len = len(Molecule.filter_element(self.atoms, "O"))
+            formula += f"O{o_len if o_len > 1 else ''}"
+
+        for element in list(sorted(elements)):
+            if element not in ["C", "H", "O"]:
+                num = len(Molecule.filter_element(self.atoms, element))
+                formula += f"{element}{num if num > 1 else ''}"
+
+        return formula
+
+    @property
+    def molecular_weight(self) -> float:
+        if not self.locked:
+            raise UnlockedMolecule
+
+        return sum(atom.weight for atom in self.atoms)
diff --git a/src/codewars/cipher_helper.py b/src/codewars/cipher_helper.py
new file mode 100644
index 0000000..acad08a
--- /dev/null
+++ b/src/codewars/cipher_helper.py
@@ -0,0 +1,32 @@
+class VigenereCipher(object):
+    def __init__(self, key: str, alphabet: str):
+        self.key = key
+        self.alphabet = alphabet
+
+    def encode(self, text):
+        encoded_text = ""
+
+        for idx, c in enumerate(text):
+            alph_position = self.alphabet.find(c)
+            if alph_position == -1:
+                encoded_text += c
+                continue
+            shift = self.alphabet.find(self.key[idx % len(self.key)])
+
+            encoded_text += self.alphabet[(alph_position + shift) % len(self.alphabet)]
+
+        return encoded_text
+
+    def decode(self, text):
+        encoded_text = ""
+
+        for idx, c in enumerate(text):
+            alph_position = self.alphabet.find(c)
+            if alph_position == -1:
+                encoded_text += c
+                continue
+            shift = self.alphabet.find(self.key[idx % len(self.key)])
+
+            encoded_text += self.alphabet[(alph_position - shift) % len(self.alphabet)]
+
+        return encoded_text
diff --git a/src/exercises/dog.py b/src/exercises/dog.py
index d9bdf4a..5a115ee 100644
--- a/src/exercises/dog.py
+++ b/src/exercises/dog.py
@@ -72,3 +72,5 @@ print(dog2.bark(3))
 print(dog2.is_puppy())
 print(Dog.amount_of_dogs)
 print(dog2 == dog1)
+
+print("is a dog", isinstance(dog1, Dog))
diff --git a/src/exercises/fetcher_protocol.py b/src/exercises/fetcher_protocol.py
new file mode 100644
index 0000000..d4589ee
--- /dev/null
+++ b/src/exercises/fetcher_protocol.py
@@ -0,0 +1,39 @@
+from dataclasses import dataclass
+from typing import Protocol
+
+
+@dataclass
+class CodeWarsUser:
+    username: str
+
+
+class UserFetcher(Protocol):
+    @staticmethod
+    def get_user(username: str) -> CodeWarsUser:
+        return CodeWarsUser(username)
+
+
+class CodewarsAdapter:
+    @staticmethod
+    def get_user(username: str) -> CodeWarsUser:
+        return CodeWarsUser(username)
+
+
+class FakeAdapter:
+    @staticmethod
+    def get_user(username: str) -> CodeWarsUser:
+        return CodeWarsUser(username)
+
+
+class WrongAdapter:
+    pass
+
+
+fetchers: list = []
+
+fetchers.append(CodewarsAdapter())
+fetchers.append(FakeAdapter())
+fetchers.append(WrongAdapter())
+
+for fetcher in fetchers:
+    print(fetcher.get_user("user name"))
diff --git a/src/order5_initial/main.py b/src/order5_initial/main.py
index 5ea6cd2..a512c0b 100644
--- a/src/order5_initial/main.py
+++ b/src/order5_initial/main.py
@@ -208,7 +208,6 @@ def main() -> None:
     ]
 
     for filename in files:
-
         BASE_DIR = Path(__file__).parent
         file_path = BASE_DIR / "data" / filename
 
diff --git a/src/testing/catching_exeptions.py b/src/testing/catching_exeptions.py
index b040155..cebeb6e 100644
--- a/src/testing/catching_exeptions.py
+++ b/src/testing/catching_exeptions.py
@@ -23,7 +23,6 @@ def double_integers(data: list[int]) -> list[int]:
 
 
 if __name__ == "__main__":
-
     data = [1, 2, 3]
     result = double_integers(data)
     print(result)
diff --git a/src/testing/pandas_filter_rows.py b/src/testing/pandas_filter_rows.py
index c929df1..f694aba 100644
--- a/src/testing/pandas_filter_rows.py
+++ b/src/testing/pandas_filter_rows.py
@@ -27,7 +27,6 @@ def filter_dataframe(df, col, func):
 
 
 if __name__ == "__main__":
-
     df = pd.DataFrame(
         {
             "A": list(range(0, 10)),