Irreducibility y is accessible from x: access t,Pt(x,y)>0 communicate .x communicates with y: 。x is accessible from y ·y is accessible from x MC is irreducible:all pairs of states communicate communicating classesIrreducibility • y is accessible from x: • x communicates with y: • x is accessible from y • y is accessible from x • MC is irreducible: all pairs of states communicate x y access communicate 1 2 1 2 1 3 2 3 3 4 1 4 3 4 1 4 communicating classes 9t, Pt (x, y) > 0