In this paper we introduce several new categorical notions and give many examples. We prove that the moduli space of stability conditions on the derived category of representations of K(l), the l-Kronecker quiver, is biholomorphic to C × H for l ≥ 3. This produces an example of semi-orthogonal decomposition, SOD, T = T1, T2 , where Stab(T ) is not biholomorphic to Stab(T1) × Stab(T2) (whereas Stab(T1 ⊕ T2) ∼ = Stab(T1) × Stab(T2) when rank(K0(Ti)) < +∞).These calculations suggest a new notion of a norm, which strictly increases on {D b (K(l))} l≥2 . To a triangulated category T which has property of a phase gap we attach a non-negative number T ε . Natural assumptions on a SOD T = T1, T2 imply T1, T2 ε ≥ max{ T1 ε , T2 ε }.Using the norm we define a non-trivial topology on the set of equivalence classes of triangulated categories with a phase gap, in which the set of discrete derived categories is a discrete subset, whereas the rationality of a smooth surface S ensures thatViewing D b (K(l)) as a non-commutative curve, we observe that it is reasonable to count noncommutative curves in any category which lies in a small neighborhood (w.r. to our topology) of a given non-commutative curve. Examples show that this idea (non-commutative curve-counting) opens directions to new categorical structures and connections to number theory and classical geometry. We give a general definition, which specializes to the non-commutative curve-counting invariants. In an example arising on the A side we specialize our definition to non-commutative Calabi-Yau curve-counting, where the entities we count are a Calabi-Yau modification of D b (K(l)).In the last section we speculate that one might consider a holomorphic family of categories, introduced by Kontsevich, as a non-commutative extension with the norm, introduced here, playing a role similar to the classical notion of degree of an extension in Galois theory.Aut(D b (P 2 )) l