1. A method of processing a query at a computer system comprising one or more processors and a memory storing one or more programs for execution of the method by the one or more processors, the method comprising: building a query tree based on the query; grouping at least some nodes of the query tree into a group of nodes based on an operator node that is a parent of the at least some nodes, the group of nodes retaining the functionality of the operator node; eliminating the operator node by replacing the operator node with the group of nodes in the tree; and traversing the tree to obtain a result list from a search index responsive to the query.