In one embodiment, a method includes accessing a model of a set of nodes including a session node and multiple linked nodes linked to the session node. The linked nodes include parent nodes and child nodes. A parent node links one or more child nodes to the session node, and a child node has one or more parent nodes linking the child node to the session node. The method includes generating a probability distribution for the set of nodes that distributes probabilities to all linked nodes within a predetermined number of links from the session node. Each child node receives from each of its parent nodes a predetermined fraction of a probability distributed to the parent node, and the parent node uniformly distributes to each of its child nodes the predetermined fraction of the probability distributed to the parent node.
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