Autumn will come after summer为什么不用is coming 而用will come,不是用现

Autumn will come after summer为什么不用is coming 而用will come,不是用现 He will come ( )autumn My brother is coming to see me.He will come here 为什么用in a fe that he will come is ture.中为什么is是谓语,will come不是 he can come now.中come为什么不用是coming?后面不是有now就要用进行时态吗? （come ,coming）to my birthday party,will you?要用哪个?为什么?主要是为什么? he is come 用he will come back行不行? it is coming soon还是it will come soon is coming 和will come 的区别是什么? They will come back（in）two days.为什么不用after? And none will come after be coming和will come的区别