The ancient rule was to stand upright, stand upright, stand upright, stand upright and love, that is, the son of the wife should be the first choice, and the eldest son should be the second, and the one who can't stand capable should stand upright.
The worst thing is that Cao Cao's first wife was Mrs. Ding, who had no children but raised his eldest son, Cao Ang, so Cao Ang can be regarded as both the eldest son and the eldest son. But unfortunately, Ding Furen divorced Cao Cao because Cao Cao died in Wancheng (yes, you are not mistaken, Cao Cao asked her to find a good man and get married)
Cao Cao's second wife is Mrs. Bian, who took up the post in the right order, and gave birth to Cao Pi, Cao Zhang, Cao Zhi and Cao Xiong, which is the new generation's first son. Cao Zhang values martial arts over literature, and Cao Xiong is sickly, so the position of the prince can only be from Cao Pi and Cao Zhi.