   \draw[very thick, <-] (V0\x)  -- (P0\x) node(xline)[right] {};   \draw[very thick, <-] (V0\x)  -- (P0\x) node(xline)[right] {};   \draw[lightgray] (V0\x)  -- (V0\x) node(xline)[right] {};   \draw[lightgray] (V0\x)  -- (V0\x) node(xline)[right] {};   