Every homology cylinder is obtained from Jacobi diagrams by clasper surgery. The surgery map $\mathfrak{ s} \colon \mathcal{ A}_n^c \to Y_n\mathcal{ IC}_{ g,1}/Y_{ n+1}$ is surjective for $n \geq 2$, and its kernel is closely related to the symmetry of Jacobi diagrams. We determine the kernel of $\mathfrak{ s}$ restricted to the 1-loop part after taking a certain quotient of the target. Also, we introduce refined versions of the AS and STU relations among claspers and study the abelian group $Y_n\mathcal{ IC}_{ g,1}/Y_{ n+2}$ for $n \geq 2$.
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