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Abstract Recent progress in the deformation theory of Calabi–Yau varieties $$Y$$ with canonical singularities has highlighted the key role played by the higher Du Bois and higher rational singularities, and especially by the so-called $$k$$-liminal singularities for $$k\ge 1$$. The goal of this paper is to show that certain aspects of this study extend naturally to the $$0$$-liminal case as well, that is, to Calabi–Yau varieties $$Y$$ with Gorenstein log canonical, but not canonical, singularities. In particular, we show the existence of first order smoothings of $$Y$$ in the case of isolated $$0$$-liminal hypersurface singularities, and extend Namikawa’s unobstructedness theorem for deformations of singular Calabi–Yau three-folds $$Y$$ with canonical singularities to the case where $$Y$$ has an isolated $$0$$-liminal lci singularity under suitable hypotheses. Finally, we describe an interesting series of examples. 

We study deformations of certain crepant resolutions of isolated rational Gorenstein singularities. After a general discussion of the deformation theory, we specialize to dimension $$3$$ and consider examples which are good (log) resolutions as well as the case of small resolutions. We obtain some partial results on the classification of canonical threefold singularities that admit good crepant resolutions. Finally, we study a noncrepant example, the blowup of a small resolution whose exceptional set is a smooth curve. Comment: 35 pages, 3 figures; v6 - final version 

Higher rational and higher Du Bois singularities have recently been introduced as natural generalizations of the standard definitions of rational and Du Bois singularities. In this note, we discuss these properties for isolated singularities, especially in the locally complete intersection (lci) case. First, we reprove the fact that a $k$-rational isolated singularity is $k$-Du Bois without any lci assumption. For isolated lci singularities, we give a complete characterization of the $k$-Du Bois and $k$-rational singularities in terms of standard invariants of singularities. In particular, we show that $k$-Du Bois singularities are $(k-<\#comment/>1)$-rational for isolated lci singularities. In the course of the proof, we establish some new relations between invariants of isolated lci singularities and show that many of these vanish. The methods also lead to a quick proof of an inversion of adjunction theorem in the isolated lci case. Finally, we discuss some results specific to the hypersurface case. 

Abstract The goal of this paper is to describe certain nonlinear topological obstructions for the existence of first-order smoothings of mildly singular Calabi–Yau varieties of dimension at least$$4$$. For nodal Calabi–Yau threefolds, a necessary and sufficient linear topological condition for the existence of a first-order smoothing was first given in [Fri86]. Subsequently, Rollenske–Thomas [RT09] generalized this picture to nodal Calabi–Yau varieties of odd dimension by finding a necessary nonlinear topological condition for the existence of a first-order smoothing. In a complementary direction, in [FL22a], the linear necessary and sufficient conditions of [Fri86] were extended to Calabi–Yau varieties in every dimension with$$1$$-liminal singularities (which are exactly the ordinary double points in dimension$$3$$but not in higher dimensions). In this paper, we give a common formulation of all of these previous results by establishing analogues of the nonlinear topological conditions of [RT09] for Calabi–Yau varieties with weighted homogeneousk-liminal hypersurface singularities, a broad class of singularities that includes ordinary double points in odd dimensions.