Fenichel, N. (1979). Geometric singular perturbation theory for ordinary differential equations. Journal of Differential Equations, 31(1), 53–98. doi:10.1016/0022-0396(79)90152-9.
Not read: a lawful open copy exists but could not be fetched on 2026-10-27 (see the status note). The summary is drawn from what the work is standardly cited for and from the exchange’s description of it. A reading should check it first.
Why this is here
A12 and A13 gave Tikhonov and Fenichel as “the precise conditions for an effective lower-dimensional dynamics to exist”, the mathematical core of CLAIM-478: under them the relation x ≈ h(y) becomes a constraint on the fast variables. The record holds Bousquet et al.’s singular- perturbation account of near-decomposability (LIT-1292), which neither reply cited. Tikhonov (1952) is named, not registered.