不定式有三种时态：一般时、进行时和完成时
He is believed to come.(=It is believed that he will come.) 要来,还没来
He is believed to be coming.(=It is believed that he is coming.) 正在来路上
He is believed to have come.(= It is believed that he has come.) 已经来了
相应地,做后置定语也有三种形式
The professor to come school is our new headmaster.
The professor to be coming school is our new headmaster.
The professor to have come school is our new headmaster.