interface value on the error equation

https://www.jstor.org/stable/pdf/2157482.pdf, here I have a problem in last equation of (2.6) in section (2.1). When they are considering error equation on the interface $Gamma$ they get $e_v^{(n)} = delta_n$, where $delta_n = lambda_n – lambda_{n-1}$(Here I use there definition of $delta_2 = lambda_2-lambda_1$, given below equation (2.7)).

1. My problem is how $e_v^{(n)} = delta_n$ on the interface $Gamma$?

If I calculate $e_v^{(n)}$ on $Gamma,$ I find something like this, $e_v^{(n)} = v^{(n)} – v|_{Gamma} = lambda_n – v|_{Gamma}$ = $lambda_n -lambda_{n-1} + lambda_{n-1} – v|_{Gamma}$ = $delta_n – e_{v}^{(n-1)}.$

2. Another problem is that the algorithm in section (2.1) start form $n=1$, then whats the value $e_v^{(1)}$ on the interface? (from the given definition $e_v^{(1)} = delta_1$, but $delta_1$ is not defined. )

Thanking you.