In a planning system, the function of the third component is to detect when a solution to problem has been found.
In a typical planning system, the third component often refers to the plan execution or plan enactment phase. The correct answer would depend on the specific context of the planning system in question. However, a general answer could be:
“The function of the third component of the planning system is to execute or enact the plan generated during the planning phase. This involves implementing the actions outlined in the plan, monitoring their progress, and adjusting as necessary to achieve the desired goals.”