“…The details are beyond the scope of the survey apart from the fact, due to Levine and Ruberman, that if X is a smooth 4-manifold with the integral homology of S 1 × S 3 , Y ⊂ X is a 3-dimensional submanifold, and s X is the spin-c structure on Y induced from X, then a correction term d(Y, s X ) ∈ Q can be defined and only depends on X and on the homology class y := [Y ] ∈ H 3 (X) [88, Theorem 1.1]; the resulting invariant is denoted d(X, y). Taking X to be M K , the result of surgery on a smooth 2-knot K ⊂ S 4 , leads to the following definition, which is due to Levine and Ruberman [88]. The d-invariant vanishes for ribbon 2-knots and obstructs invertibility and amphicheirality [88,Section 6]; it also obstructs 0-concordance [126].…”