Definition: In this task, you are given two phrases: Head and Tail, separated with <sep>. The Head and the Tail events are short phrases possibly involving participants. The names of specific people have been replaced by generic words (e.g., PersonX, PersonY, PersonZ). PersonX is always the subject of the event. You have to determine whether the Head happens before the Tail or not. Classify your answers into "Yes" and "No". The phrase may also contain "___", a placeholder that can be an object, a person, and/or an action.

Positive Example 1 -
Input: Head: PersonX swims at the local pool<sep>Tail: PersonX learns a new way of swimming
Output: Yes

Positive Example 2 -
Input: Head: PersonX acts as PersonY intermediary<sep>Tail: assist and protect PersonY's interests
Output: No

Negative Example 1 -
Input: Head: PersonX acts like a PersonY<sep>Tail: to observe
Output: Yes

Negative Example 2 -
Input: Head: PersonX tries to fix it<sep>Tail: PersonX orders new glass
Output: No

Now complete the following example -
Input: Head: PersonX achieves PersonY understanding<sep>Tail: PersonX gains knowledge.
Output: No