Minor fix in typo (aimacode#779)

Author: alanoli

search.ipynb

@@ -143,15 +143,15 @@
    "source": [
     "The `Node` class has nine methods.\n",
     "\n",
-    "* `__init__(self, state, parent, action, path_cost)` : This method creates a node. `parent` represents the the node that this is a successor of and `action` is the action required to get from the parent node to this node. `path_cost` is the cost to reach current node from parent node.\n",
+    "* `__init__(self, state, parent, action, path_cost)` : This method creates a node. `parent` represents the node that this is a successor of and `action` is the action required to get from the parent node to this node. `path_cost` is the cost to reach current node from parent node.\n",
     "\n",
     "* `__repr__(self)` : This returns the state of this node.\n",
     "\n",
     "* `__lt__(self, node)` : Given a `node`, this method returns `True` if the state of current node is less than the state of the `node`. Otherwise it returns `False`.\n",
     "\n",
-    "* `expand(self, problem)` : This methods lists all the neighbouring(reachable in one step) nodes of current node. \n",
+    "* `expand(self, problem)` : This method lists all the neighbouring(reachable in one step) nodes of current node. \n",
     "\n",
-    "* `child_node(self, problem, action)` : Given an `action`, this methods returns the immediate neighbour that can be reached with that `action`.\n",
+    "* `child_node(self, problem, action)` : Given an `action`, this method returns the immediate neighbour that can be reached with that `action`.\n",
     "\n",
     "* `solution(self)` : This returns the sequence of actions required to reach this node from the root node. \n",
     "\n",