this theorem showed that under the combined action of three operators on a physical event: p, the parity operator, which performed a reflection; c, the charge conjugation operator, which replaced particles by anti-particles; and t, which performed a time reversal, the result would be another possible physical event.

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This theorem showed that under the combined action of three operators on a physical event: P, the parity operator, which performed a reflection; C, the charge conjugation operator, which replaced particles by anti-particles; and T, which performed a time reversal, the result would be another possible physical event.