In this paper we enumerate the skew braces of size p 2 q for p, q odd primes by the classification of regular subgroups of the holomorph of the groups of size p 2 q. In particular, we provide explicit formulas for the skew braces of abelian type.Proof. The groups H, L and G c,θ are regular. If G c,β 0,r and G d,β 0,r are conjugate by some h ∈ Aut(A), then h normalizes β 0,r and so it centralizes it. So h(σ) c β 0,r = σ c β 0,r (mod ǫ, τ ). Then σ c β 0,r = σ d β 0,r (mod ǫ, τ ) which implies that c = d. The same argument applies if θ = α 1,1 β 0,r .Let G be a regular subgroup of Hol(A) such that |π 2 (G)| = p. According to Table 16 we need to discuss three cases.Assume that π 2 (G) = α 1,1 . Then the kernel has order pq and so, up to conjugation by a power of α 1,1 we can assume that G = ǫ, σ n τ m , σ a τ b α 1,1 . By condition (K) we have n = 0. So G = ǫ, τ, σ a α 1,1 and G is conjugate to H by α 0,a −1 .Assume that π 2 (G) = β 0,r . Then G has the following standard presentation:If n = 0, we conjugate G by α − m n ,1 and then by α 0,b −1 and we get L. If n = 0 we have G = ǫ, τ, σ b β 0,r = G b,β 0,r .Assume that π 2 (G) = α 1,1 β 0,r . Then

We adapt the commutator theory of universal algebra to the particular setting of racks and quandles, exploiting a Galois connection between congruences and certain normal subgroups of the displacement group. Congruence properties such as abelianness and centrality are reflected by the corresponding relative displacement groups, and so do the global properties, solvability and nilpotence. To show the new tool in action, we present three applications: non-existence theorems for quandles (no connected involutory quandles of order 2 k , no latin quandles of order ≡ 2 (mod 4)), a non-colorability theorem (knots with trivial Alexander polynomial are not colorable by latin quandles), and a strengthening of Glauberman's results on Bruck loops of odd order.

In the paper we describe the class of principal quandles and we show that connected quandles can be decomposed as a disjoint union of principal quandles. We also prove that simple affine quandles are finite and they can be characterized among finite simple quandles by several different equivalent properties, such as for instance being doubly homogeneous (i.e. having a doubly transitive automorphism group). A complete description of finite doubly-homogeneous quandles is provided extending the result of [34] and solving [3, Problem 6.7]. We also provide a classification of connected cyclic quandles with several fixed points independently from [23].