diff --git a/Hypertension.rb b/Hypertension.rb
index a89fc75..252f99d 100644
--- a/Hypertension.rb
+++ b/Hypertension.rb
@@ -83,7 +83,7 @@ def planning(tasks, level = 0)
           puts "#{'  ' * level.pred}#{method}(#{current_task.join(' ')})" if @debug
           # Every unification is tested
           __send__(method, *current_task) {|subtasks|
-            subtasks.each {|t| [(@index += 1 if @domain[t[0]]), t]}
+            subtasks.map! {|t| [(@index += 1 if @domain[t[0]]), t]}
             new_index = @index
             if plan = planning(subtasks.concat(tasks), level)
               @decomposition.unshift("#{index} #{task_name} #{current_task.join(' ')} -> #{method[task_name.size+1..-1]} #{(old_index+1..new_index).to_a.join(' ')}")