We consider differentiable maps having an invariant torus with normal behav
iour and a central part. We prove the existence and regularity of strong-st
able manifolds and regularity with respect to the parameters. Then we prove
a lambda lemma in this setting for C-2 maps. These results have applicatio
ns in the study of diffusion problems, including Arnol'd diffusion. AMS cla
ssification scheme numbers: 58F30, 34C35, 34C37.