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  With Partial Indexes:

   A partial index is any index with the one or more of the following
   attributes.

       . Created with a FOR condition
       . Is Roll-Your-Own
       . Was created UNIQUE

   Mach SIx will only optimize a query condition using one of the above
   types of indexes when the current order is set to that index.  The
   following example shows, when a partial index will and will not be used
   to optimize a query.

      USE Customers

      INDEX ON Age TO Partial FOR Married

      SET INDEX TO State, Name, Partial

      SET ORDER TO 3

      // Fully optimizable with order set to Partial index
      ? Is_Optimize()                                          //...2

      ? "Counting..."
      COUNT TO nCount
      ? "Poof!"

      ? nCount

      SET ORDER TO 1

      // Count not optimizable with order set to 1
      ? Is_Optimize()                                          //...0

      ? "Counting..."
      COUNT TO nCount
      ? "Finally..."

      ? nCount