This paper defines the class of sampling problems SampP (see Definition 11). It requires that the probability of the generated samples $C_x$ is close to the target probability $D_x$ within an error $\epsilon$. The definition of this admissible error is: $$ \lVert C_s - D_x \rVert \le \epsilon $$ Now, what I do not clearly understand is what this norm is: $L_1$, $L_2$, or something else? It is not stated. There are passages relying on the triangular inequality, so I can rule out the possibilitytell that the definition holds for (whateverit must refer to some norm)(EDITED: functions not fulfilling the triangular equality) that has a triangle inequality. Do you have any suggestion?