procedure mgram( t : patricia; m, k : integer; var pq : queue );
        {*** Should start with an empty (minimum) priority queue,
             on returning, the priority queue contains the k most
             frequent m-grams  ***}
     begin
     if wt(t) >= inspect( pq ) or
	size( pq ) < k then begin
          if t^.level >= BITS_PER_CHAR*m then begin
               if size( pq ) = k then delete( pq );
               insert( t, pq )
               end
          else begin
               if wt( t^.left ) > wt( t^.right ) then
                    begin mgram(t^.right,m,k,pq);  mgram(t^.left,m,k,pq) end
               else begin mgram(t^.left,m,k,pq);  mgram(t^.right,m,k,pq) end
               end
          end
     end;