What are difference between A and AO algorithm?

# Initialise the graph to start node # Traverse the graph following the current path accumulating nodes that have not yet been expanded or solved # Pick any of these nodes and expand it and if it has no successors call this value FUTILITY otherwise calculate only f' for each of the successors. # If f' is 0 then mark the node as SOLVED # Change the value of f' for the newly created node to reflect its successors by back propagation. # Wherever possible use the most promising routes and if a node is marked as SOLVED then mark the parent node as SOLVED. # If starting node is SOLVED or value greater than FUTILITY, stop, else repeat from 2.