Let $x_i,y_i \in \mathbb{R}$. Consider the following set of inequalities. \begin{align} x_1-x_2 &\leqslant y_1 \\ x_2-x_3 &\leqslant y_2 \\ &\vdots \\ x_{n-1}-x_n &\leqslant y_{n-1} \\ x_n-x_1 &\leqslant y_n \\ \end{align} If they are consistent, necessarily $\sum_{i=1}^n y_i \geqslant 0$.
Is that also a sufficient condition of feasibility?