(M2-1) $s_n=\text{Input} \text{to} \text{stage} n$

The input to stage n. This is also the output from stage $n+1.$

(M2-2) $d_n=\text{Decision} \text{at} \text{stage} n$

The decision at stage n.

(M2-3) $r_n=\text{Return} \text{at} \text{stage} n$

The return function, usually profit or loss, at stage n.

(M2-4) $s_{n-1}=\text{Output} \text{from} \text{stage} n$

The output from stage n. This is also the input to stage $n-1.$

(M2-5) $t_n=\text{Transformation} \text{function} \text{at} \text{stage} n$

A transformation function that allows us to go from one stage to another.

(M2-6) $s_{n-1}=t_n\left(s_n,d_n\right)$

The general relationship that shows how the output from any stage is a function of the input to the stage and the decisions made at that stage.

(M2-7) $f_n=\text{Total} \text{return} \text{at} \text{stage} n$

This equation gives the total return (profit or costs) at any stage. It is obtained by summing the return at each stage, $r_n.$