diff --git a/python_symb/Expressions/expr.py b/python_symb/Expressions/expr.py
index d26d828..eac9577 100644
--- a/python_symb/Expressions/expr.py
+++ b/python_symb/Expressions/expr.py
@@ -85,11 +85,9 @@ class Expr(Tree):
             case Expr(BinOperator() as op, [left, right]):
                 op_name = op.name if not(implicit_mul and op == Mul) else ''
                 if op.precedence < parent_precedence:
-                    print("hehehe")
-                    print(self, op.precedence, parent_precedence)
-                    return f"({left.to_infix_str(op.precedence)}{op_name}{right.to_infix_str(op.precedence)})"
+                    return f"({left.to_infix_str(op.precedence, implicit_mul)}{op_name}{right.to_infix_str(op.precedence, implicit_mul)})"
                 else:
-                    return f"{left.to_infix_str(op.precedence)}{op_name}{right.to_infix_str(op.precedence)}"
+                    return f"{left.to_infix_str(op.precedence, implicit_mul)}{op_name}{right.to_infix_str(op.precedence, implicit_mul)}"
 
 
 
@@ -123,8 +121,18 @@ class Expr(Tree):
         other_expr = other if isinstance(other, Expr) else Expr(other)
         return Expr.bin_op_constructor(other_expr, self, Mul)
 
+    def __pow__(self, other):
+        other_expr = other if isinstance(other, Expr) else Expr(other)
+        return Expr.bin_op_constructor(self, other_expr, Exp)
+
+    def __neg__(self):
+        return Expr(Mul, [Expr(-1), self])
+
     def __sub__(self, other):
-        return Expr.bin_op_constructor(self, other, Min)
+        return self + (-other)
+
+    def __rsub__(self, other):
+        return other + (-self)
 
     def __hash__(self):
         """
@@ -155,52 +163,41 @@ class Expr(Tree):
         """temporary"""
         return self.bad_eq(other)
 
+    def delete_node(self, node: Expr) -> Expr:
+        """
+        return a new expression without all occurences of the node (with the equality defined by the __eq__ method)
+
+        :param node: node to delete everywhere
+        """
+        match self:
+
+            case Expr(value) if self.is_leaf:
+                if self == node:
+                    raise "Cannot delete a leaf node, don't"
+                else:
+                    return self
+
+            case Expr(UnaryOperator() as op, [child]):
+                if child == node:
+                    raise ValueError("Cannot delete a node that is the child of a unary operator, don't.")
+                else:
+                    return Expr(op, [child.delete_node(node)])
+
+            case Expr(BinOperator() as op, [left, right]):
+                if left == node:
+                    return right
+                elif right == node:
+                    return left
+                else:
+                    return Expr(op, [left.delete_node(node), right.delete_node(node)])
+
+            case _:
+                raise ValueError(f'Invalid type: {type(self)}')
 
-def test():
-    x, y = var('x'), var('y')
-    a, b = var('a'), var('b')
-    def test1():
-        expr1 = x + y
-        expr2 = 5+x
-        print(expr1 + expr2)
 
 
-    def test2():
-        from python_symb.MathTypes.operator_file import Sin
-        expr = Sin(x+y)
-        print(expr)
 
-    def test_eq():
-        expr = x + y + 3
-        expr2 = 3 + x + y
-        print("----")
-        print(expr)
-        print(expr2)
-        print(expr == expr2)
 
-    def test_return_to_string():
-        expr = x+y
-        new_expr = 5*expr
-        print(new_expr)
-        print(f"new_expr: {new_expr.to_infix_str()}")
-
-        expr2 = x*x*x + y*y*y
-        print(expr2)
-        print(f"expr2: {expr2.to_infix_str()}")
-
-
-    print("test1")
-    test1()
-    print("test2")
-    test2()
-    print("test_eq")
-    test_eq()
-    print("test_return_to_string")
-    test_return_to_string()
-
-
-if __name__ == '__main__':
-    test()
 
 
 
diff --git a/python_symb/MathTypes/operator_file.py b/python_symb/MathTypes/operator_file.py
index 7a7f862..8a7a46b 100644
--- a/python_symb/MathTypes/operator_file.py
+++ b/python_symb/MathTypes/operator_file.py
@@ -7,9 +7,13 @@ class Operator(Symbols):
     """
     Represent an operator, like +, *, sin, anything that can be applied to an expression
     """
+    # Store all the instances of Operator, used in the parser
     instances = {}
+    # The deconstruct operator of a repeated operator is used to deconstruct an expression (x+y)^2 -> (x+y)*(x+y)
+    # Mul is the deconstruct operator of Add
+    deconstruct_op_dict = {}
 
-    def __init__(self, name: str, precedence: int, call: Callable, repeated_op: Operator = None):
+    def __init__(self, name: str, precedence: int, call: Callable, repeated_op: BinOperator = None):
         """
         :param name of the operator
         :param precedence: precedence of the operator, higher is better
@@ -24,9 +28,16 @@ class Operator(Symbols):
         self.repeated_op = repeated_op
         Operator.instances[name] = self
 
+        if repeated_op:
+            Operator.deconstruct_op_dict[repeated_op] = self
+
     def __repr__(self):
         return f'{self.name}'
 
+    @property
+    def deconstruct_op(self):
+        return Operator.deconstruct_op_dict.get(self, None)
+
 
 class UnaryOperator(Operator):
     """
@@ -53,7 +64,7 @@ class BinProperties:
     """
 
     def __init__(self, associative: bool, commutative: True,
-                 left_distributivity: Set[str], right_distributivity: Set[str]):
+                 left_distributivity: Set[str], right_distributivity: Set[str], neutral_element=None, absorbing_element=None):
         """
         :param associative: True if the operator is associative
         :param commutative: True if the operator is commutative
@@ -72,18 +83,29 @@ class BinProperties:
         self.commutative = commutative
         self.left_distributive = left_distributivity
         self.right_distributive = right_distributivity
+        self.neutral_element = neutral_element
+        self.absorbing_element = absorbing_element
 
 
 class BinOperator(Operator):
     """
     Represent a binary operator, like +, *, etc...
     all operators that take two arguments
+
     """
 
     # Used to store all the instances of BinOperator, used in the parser
     instances = {}
 
-    def __init__(self, name: str, precedence: int, properties: BinProperties, call: Callable, repeated_op: Operator = None ):
+    def __init__(self, name: str, precedence: int, properties: BinProperties, call: Callable, repeated_op: BinOperator = None):
+        """
+        :param name: name of the operator
+        :param precedence: precedence of the operator, higher is better
+        :param properties: properties of the operator
+        :param call: function to apply the operator
+        :param repeated_op: if you repeat the operator what do you get ? (for exemple a+a+a+a -> 4*a, the repeated_op of Add is Mul)
+        :param deconstruct_op: if you deconstruct the operator what do you get ? (for exemple 4*a -> a+a+a+a, the deconstruct_op of Mul is Add)
+        """
         BinOperator.instances[name] = self
         super().__init__(name, precedence, call, repeated_op)
         self.properties = properties
@@ -99,13 +121,13 @@ class BinOperator(Operator):
 """
 Generic operators
 """
-ExpProperties = BinProperties(False, False, set(), set())
+ExpProperties = BinProperties(False, False, set(), set(), 1)
 Exp = BinOperator('^', 4, ExpProperties, lambda x, y: x ** y)
 
-MulProperties = BinProperties(True, True, {'+'}, {'+'})
+MulProperties = BinProperties(True, True, {'+'}, {'+'}, 1, 0)
 Mul = BinOperator('*', 3, MulProperties, lambda x, y: x * y, Exp)
 
-AddProperties = BinProperties(True, True, set(), set())
+AddProperties = BinProperties(True, True, set(), set(), 0)
 Add = BinOperator('+', 2, AddProperties, lambda x, y: x + y, Mul)
 
 
diff --git a/python_symb/TreeModification/basic_modif.py b/python_symb/TreeModification/basic_modif.py
index ce71a39..ce86013 100644
--- a/python_symb/TreeModification/basic_modif.py
+++ b/python_symb/TreeModification/basic_modif.py
@@ -1,6 +1,6 @@
 from python_symb.Expressions.expr import Expr
 from python_symb.MathTypes.symbols import Var
-from python_symb.MathTypes.operator_file import Operator, BinOperator, Add, Mul
+from python_symb.MathTypes.operator_file import Operator, BinOperator, Add, Mul, Exp
 from typing import Union
 
 
@@ -23,10 +23,10 @@ def expand(expr: Expr) -> Expr:
         return expr
 
     match expr:
-        case Expr(BinOperator() as Op1, [Expr(Op2, op2_children), right]) if Op2.name in Op1.properties.left_distributive:
+        case Expr(BinOperator() as Op1, [Expr(BinOperator() as Op2, op2_children), right]) if Op2.name in Op1.properties.left_distributive:
             return expand(Expr(Op2, [Expr(Op1, [expand(op2_child), expand(right)]) for op2_child in op2_children]))
 
-        case Expr(BinOperator() as Op1, [left, Expr(Op2, op2_children)]) if Op2.name in Op1.properties.right_distributive:
+        case Expr(BinOperator() as Op1, [left, Expr(BinOperator() as Op2, op2_children)]) if Op2.name in Op1.properties.right_distributive:
             return expand(Expr(Op2, [Expr(Op1, [expand(left), expand(op2_child)]) for op2_child in op2_children]))
 
         case Expr(BinOperator() as Op, [left, right]):
@@ -53,7 +53,7 @@ def _regroup(expr: Expr, focus_op: BinOperator) -> Expr:
 
     # Motifs : Key : (Expr) -> Value : int
     # represent number of times the expression appears in the expression,
-    # custom hash make for instance x+y and y+x the same when counting
+    # custom expr hash make for instance x+y and y+x the same when counting in motifs
     motifs = {}
 
     def collect_motifs(expr: Expr):
@@ -76,11 +76,16 @@ def _regroup(expr: Expr, focus_op: BinOperator) -> Expr:
     def reconstruct(tuple_motifs):
         match tuple_motifs:
             case [(expr, int(a))]:
-                if focus_op.repeated_op.properties.commutative:
+                if a == focus_op.repeated_op.properties.neutral_element:
+                    return expr
+                elif focus_op.repeated_op.properties.commutative:
                     return Expr(focus_op.repeated_op, [Expr(a), expr])
                 return Expr(focus_op.repeated_op, [expr, Expr(a)])
+
             case [(expr, int(a)), *rest]:
-                if focus_op.repeated_op.properties.commutative:
+                if a == focus_op.repeated_op.properties.neutral_element:
+                    return Expr(focus_op, [expr, reconstruct(rest)])
+                elif focus_op.repeated_op.properties.commutative:
                     return Expr(focus_op, [Expr(focus_op.repeated_op, [Expr(a), expr]), reconstruct(rest)])
                 return Expr(focus_op, [Expr(focus_op.repeated_op, [expr, Expr(a)]), reconstruct(rest)])
 
@@ -112,42 +117,46 @@ def regroup(expr: Expr, focus_op: BinOperator) -> Expr:
     return expr
 
 
-def test():
+def ungroup(expr: Expr, focus_op: BinOperator) -> Expr:
+    """
+    Ungroup an expression
+
+    :param expr: expression to ungroup
+    :param focus_op: operator to ungroup
+
+    exemple :
+    with focus_op = Exp
+    (x+y) ^ 2 -> (x+y)*(x+y)
+    """
+
+    def recreate(expr: Expr, nb_repeat: int) -> Expr:
+        if nb_repeat == 1:
+            return expr
+        return Expr(focus_op.deconstruct_op, [expr, recreate(expr, nb_repeat-1)])
+
+    if expr.is_leaf:
+        return expr
+
+    match expr:
+        case Expr(BinOperator() as op, [left, leaf]) if op == focus_op and isinstance(leaf.value, int):
+            return recreate(ungroup(left, focus_op), leaf.value)
+        case Expr(BinOperator() as op, [leaf, right]) if op == focus_op and isinstance(leaf.value, int):
+            return recreate(ungroup(right, focus_op), leaf.value)
+        case Expr(BinOperator() as op, [left, right]):
+            return Expr(op, [ungroup(left, focus_op), ungroup(right, focus_op)])
+
+    return expr
+
+
+
 
-    x, y = Var('x'), Var('y')
-    a, b = Var('a'), Var('b')
 
-    def test_expand():
-        expr = (x+y)*(x+y)*(x+y)
-        expr = expand(expr)
-        expr = regroup(expr, Add)
-        print(f"(x+y)*(x+y)*(x+y) -> {expr.to_infix_str()}")
-        expr = (x+y+a)*b
-        print(f"(x+y+a)*b -> {expand(expr).to_infix_str()}")
 
-    def test_regroup():
-        expr = x+2*x+y+y+2*y
-        print(f"x+2*x+y+y+2*y -> {regroup(expr, Add).to_infix_str()}")
 
-    def test_power():
-        expr = x*x*x + y*y*y
-        print(f"x*x*x -> {regroup(expr, Mul).to_infix_str()}")
 
-    def test_all():
-        expr = (x+y)*(x+y)*(x+y)
-        expanded_expr = expand(expr)
-        regrouped_expr = regroup(expanded_expr, Add)
-        print(f"(x+y)*(x+y)*(x+y) -> {regrouped_expr.to_infix_str()}")
 
 
 
 
-    test_expand()
-    test_regroup()
-    test_power()
-    #test_all()
-
-if __name__ == "__main__":
-    test()
 
 
diff --git a/python_symb/test.py b/python_symb/test.py
new file mode 100644
index 0000000..ca94884
--- /dev/null
+++ b/python_symb/test.py
@@ -0,0 +1,137 @@
+from python_symb.MathTypes.symbols import var
+from python_symb.Expressions.expr import Expr
+from python_symb.MathTypes.operator_file import Add, Mul, Exp, Sin
+from python_symb.TreeModification.basic_modif import expand, regroup, ungroup
+import time
+from functools import wraps
+
+
+def timeit(func):
+    @wraps(func)
+    def measure_time(*args, **kwargs):
+        start_time = time.time()
+        result = func(*args, **kwargs)
+        end_time = time.time()
+        print("@timefn: {} took {} seconds.".format(func.__name__, end_time - start_time))
+        return result
+    return measure_time
+
+
+# assert equal use none perfect implementation of __eq__ in expr (using weird handmade hash), be careful
+
+def create_var():
+    global x, y
+    x = var('x')
+    y = var('y')
+
+
+def test_sum(print_result=False):
+    expr = x + y
+    expr2 = 5 + x
+    if print_result:
+        print(f"expr1: {expr}")
+        print(f"expr2: {expr2}")
+
+    assert expr == Expr(Add, [Expr(x), Expr(y)])
+    assert expr2 == Expr(Add, [Expr(5), Expr(x)])
+
+
+def test_parse(print_result=False):
+    str_expr = "5*(x+y) + x*sin(y)"
+    expr = Expr.from_infix_str(str_expr)
+    if print_result:
+        print(f"expr: {expr}")
+
+    assert expr == Expr(Add, [Expr(Mul, [Expr(5), Expr(Add, [Expr(x), Expr(y)])]), Expr(Mul, [Expr(x), Expr(Sin, [Expr(y)])])])
+
+
+def test_expr_to_str(print_result=False):
+    expr = 5*(x+y) + x*Sin(y)
+    str_expr = expr.to_infix_str(implicit_mul=True)
+    str_expr_no_implicit = expr.to_infix_str(implicit_mul=False)
+
+    if print_result:
+        print(f"str_expr: {str_expr}")
+        print(f"str_expr_no_implicit: {str_expr_no_implicit}")
+
+    assert str_expr == "5(x+y)+xsin(y)"
+    assert str_expr_no_implicit == "5*(x+y)+x*sin(y)"
+
+
+def test_expand(print_result=False):
+    expr = (x+2)*(x+y)
+    expanded = expand(expr)
+    expanded_str = expanded.to_infix_str()
+    if print_result:
+        print(f"expanded: {expanded_str}")
+
+    assert expanded_str == "xx+xy+2x+2y"
+    assert expanded == Expr(Add, [Expr(Add, [Expr(Mul, [Expr(x), Expr(x)]), Expr(Mul, [Expr(x), Expr(y)])]), Expr(Add, [Expr(Mul, [Expr(2), Expr(x)]), Expr(Mul, [Expr(2), Expr(y)])])])
+
+
+def test_regroup(print_result=False):
+    expr = x+x+2*x+y+x+3*y+x
+    regrouped = regroup(expr, Add)
+    regrouped_str = regrouped.to_infix_str()
+    if print_result:
+        print(f"regrouped: {regrouped_str}")
+
+    assert regrouped_str == "6x+4y"
+    assert regrouped == Expr(Add, [Expr(Mul, [Expr(6), Expr(x)]), Expr(Mul, [Expr(4), Expr(y)])])
+
+
+def test_newton_bin(print_result=False):
+    expr = (x+y)**4
+    ungrouped = ungroup(expr, Exp)
+    expanded = expand(ungrouped)
+    expand_grouped = regroup(expanded, Add)
+    expand_grouped = regroup(expand_grouped, Mul)
+
+    if print_result:
+        print("---")
+        print("newton binomial test")
+        print("---")
+        print(f"expr: {expr.to_infix_str()}")
+        print(f"ungrouped: {ungrouped.to_infix_str()}")
+        print(f"expanded: {expanded.to_infix_str()}")
+        print(f"expand_grouped: {expand_grouped.to_infix_str()}")
+
+    assert expand_grouped == Expr(Add, [Expr(Exp, [Expr(x), Expr(4)]),Expr(Add, [Expr(Mul, [Expr(4),Expr(Mul, [Expr(Exp, [Expr(x), Expr(3)]),Expr(y)])]),Expr(Add, [Expr(Mul, [Expr(6),Expr(Mul, [Expr(Exp, [Expr(x), Expr(2)]),Expr(Exp, [Expr(y), Expr(2)])])]),Expr(Add, [Expr(Mul, [Expr(4),Expr(Mul, [Expr(x),Expr(Exp, [Expr(y), Expr(3)])])]),Expr(Exp, [Expr(y), Expr(4)])])])])])
+
+@timeit
+def test_big_bin_for_performance(print_result=False):
+    expr = (x+y)**11
+    print("a")
+    ungrouped = ungroup(expr, Exp)
+    print("b")
+    expanded = expand(ungrouped)
+    print("c")
+    expand_grouped = regroup(expanded, Add)
+    print("d")
+    expand_grouped = regroup(expand_grouped, Mul)
+    print("e")
+
+    if print_result:
+        print("---")
+        print("ultra big newton binomial test")
+        print("---")
+        print(f"expr: {expr.to_infix_str()}")
+        print(f"ungrouped: {ungrouped.to_infix_str()}")
+        print(f"expanded: {expanded.to_infix_str()}")
+        print(f"expand_grouped: {expand_grouped.to_infix_str()}")
+
+if __name__ == '__main__':
+    create_var()
+    print_r = True
+    test_sum(print_result=print_r)
+    test_parse(print_result=print_r)
+    test_expr_to_str(print_result=print_r)
+    test_expand(print_result=print_r)
+    test_regroup(print_result=print_r)
+    test_newton_bin(print_result=print_r)
+    test_big_bin_for_performance(print_result=print_r)
+    print("All tests passed")
+
+
+
+