In determining when a four-dimensional ellipsoid can be symplectically embedded into a ball, McDuff and Schlenk found an infinite sequence of 'ghost' obstructions that generate an infinite 'ghost staircase' determined by the even index Fibonacci numbers. The ghost obstructions are not visible for the four-dimensional embedding problem because strictly stronger obstructions also exist. We show that in contrast, the embedding constraints associated to the ghost obstructions are sharp for the stabilized problem; moreover, the corresponding optimal embeddings are given by symplectic folding.The proof introduces several techniques of independent interest, namely: (i) new applications of ideas from embedded contact homology (ECH) in the context of nodal curves, (ii) an improved version of the index inequality familiar from the theory of embedded contact homology, (iii) new applications of relative intersection theory in the context of neck stretching analysis, (iv) a new approach to estimating the ECH grading of multiply covered elliptic orbits in terms of areas and continued fractions, and (v) a new technique for understanding the ECH of ellipsoids by constructing explicit bijections between certain sets of lattice points.Contents Actually the construction in [8] only applies to compact subsets of the stabilized ellipsoid. To embed the whole product we are appealing to [23].q with gcd(p, q) = 1 and ε > 0 irrational and very small, and fix μ * > 0. Suppose that for all sufficiently small ε > 0 and generic admissible J there is a genus 0 curve C in X μ ,x with degree d, Fredholm index 0, and one negative end on {(β 1 , p)}, where gcd(d, p) = 1. Then, 3d = p + q, and for all k 0, we haveThe proof is given in § 3.6: see Proposition 3.6.1. The main point is that if C has genus 0, Fredholm index zero, and one negative end, then its Fredholm index remains zero under † In fact if the domain is an ellipsoid the two embedding problems are equivalent: see [19]. Here CP 2 (μ) denotes CP 2 with symplectic form ω scaled so that ω takes the value μ on the line L.‡ Here we assume that J is admissible, that is, adapted to the negative end of X: see § 2 for more details. † In fact, the ECH cobordism map detects buildings with ECH index 0 that may (and often do) consist of curves with both positive and negative ECH index. Further, it may not always be the case that curves with ECH index 2 and Fredholm index 0 must have double points, but as mentioned in Remark 2.2.3(ii) this is known in some situations.