Columbia subject headings:
Boundary value problems--Asymptotic theory.
Differential equations, Elliptic--Asymptotic theory.
Differential equations, Parabolic--Asymptotic theory.
Perturbation (Mathematics)
Harvard subject headings:
Differential equations.
Princeton subject headings:
Boundary value problems--Asymptotic theory.
Differential equations, Elliptic--Asymptotic theory.
Differential equations, Parabolic--Asymptotic theory.
Perturbation (Mathematics)