If eating food is subset, having energy is superset. Eat food is sufficient for having energy, but it is not necessary for having energy, since you can have energy from other way. Having energy is necessary for eating food, but is not sufficient eating food, since since you can have energy from other way. Eating food is subset, having energy is superset. But I don't feel it is a very good example, since eating food is an action, having energy is a status, these two things are hard to figure out one same characteristic.

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