Normal complex of groups

Definition
A defining ingredient::chain complex of groups $$(G_n,d_n)_{n \in \mathbb{Z}}$$ given as follows:

$$ \dots \to G_n \stackrel{d_n}{\to} G_{n-1} \stackrel{d_{n-1}}{\to} G_{n-2} \to \dots$$

is termed a normal complex of groups if, for every $$n \in \mathbb{Z}$$, the image group $$d_n(G_n)$$ is a defining ingredient::normal subgroup inside $$G_{n-1}$$.