We investigate a new algebraic structure which always gives rise to set-theoretic solution of the Yang-Baxter equation. Specifically, weak (left) brace is non-empty set $S$ endowed with two binary operations $+$ and $\circ$ such that both $(S,+)$ $(S, \circ)$ are inverse semigroups they hold \begin{align*} \circ \left(b+c\right) = a\circ b - +a\circ c \qquad \text{and} a^- + a, \end{align*} for...