User blog comment:Alemagno12/A ordinal notation/@comment-25337554-20150726094129/@comment-25337554-20150727062944

A(Ω,1)=A(Ω,A(0))=sup(A(Ω,0),A(A(Ω,0),0),A(A(A(Ω,0),0),0)...)=sup(A(Ω,0),A(Ω,0),A(Ω,0),...)=A(Ω,0)

You can use induction above two.