On coincidences of singular loci of types Σ1ᵣ and Σʳ

It is well-known that the Thom polynomial in Stiefel--Whitney classes expressing the cohomology class dual to the locus of the cusp singularity for codimension-k maps Σ1₂(k) and that of the corank-$2$ singularity for codimension-$(k-1)$ maps Σ²(k-1) coincide: both are wₖ₊₁² + wₖ wₖ₊₂. The aim of the present paper is to find out whether there is any geometric explanation to this seemingly mysterious coincidence. We thank L\'aszl\'o Feh\'er for posing us this interesting question that we answer here to the positive, and motivated by it we search for further similar coincidences of the loci of Σ1ᵣ-type and Σʳ-type singular points for a general r, but found such ones only for special classes of maps. Finally we compute the cohomology classes dual to the singularity strata for any Morin map. (This result--for holomorphic maps--was presented by Kazarian but the proof was left unpublished.)