class Node:    def __init__(self, value):        self.value = value        self.grad = 0        self._backward = lambda: None # this is defined as the forward mode is done based on the computation graph.         self._prev = set()    def __add__(self, other):        other = other if isinstance(other, Node) else Node(other)        out = Node(self.value + other.value)        out._prev = {self, other}        def _backward():            self.grad += out.grad            other.grad += out.grad        out._backward = _backward        return out    def __mul__(self, other):        other = other if isinstance(other, Node) else Node(other)        out = Node(self.value * other.value)        out._prev = {self, other}        def _backward():            self.grad += other.value * out.grad            other.grad += self.value * out.grad        out._backward = _backward        return out    def __pow__(self, n):        out = Node(self.value ** n)        out._prev = {self}        def _backward():            self.grad += n * (self.value ** (n-1)) * out.grad         out._backward = _backward        return outdef backward(node):    topo = []    visited = set()    def build_topo(v):        if v not in visited:            visited.add(v)            for child in v._prev:                build_topo(child)            topo.append(v)    build_topo(node)    node.grad = 1    for node in reversed(topo):        node._backward()# Example usagex = Node(2.0)y = x**4 + 3*x**2 + 2*xbackward(y)print(f"f(2) = {y.value}, f'(2) = {x.grad}")# Output: f(2) = 42.0, f'(2) = 58.0