Let A ⊆ R, let f : A → R be a function, and let c be a limit
point of A. Suppose that a student copied down the following
definition of the limit of f at c: “we say that limx→c f(x) = L
provided that, for all ε > 0, there exists a δ ≥ 0 such that if
0 < |x − c| < δ and x ∈ A, then |f(x) − L| < ε”. What was...