  We present a collection of simple derivations for the neutron-induced
resonance cross-sections. These formulae are commonly used to experimentally
describe the fundamental properties of resonances for neutron-rich nuclei far
from stability and to describe unbound nuclei. The main goal of this article is
to illustrate their dependencies with basic observables in order to discuss the
pertinence of experimental approaches in the derivation of their properties,
especially for "N-body" resonances.
