There are three cases: Here, e out = Pt(f ) = 0, and e in ∈ (1, N ).
for all vertices v ∈ (1, N ) there is an edge g in the chain such that v is between the endpoints of g. e will cross such an edge g. To satisfy the 1-EC property, g must share an endpoint with f , which means g is either (1, 3) or (N −2, N ).