Figures $15\mathrm{.}4\mathrm{.}2$ and $15\mathrm{.}4\mathrm{.}3,$ illustrating the Prim$-$Jarn$$k algorithm. What do thick lines and

dashed lines signify?

Figure $15\mathrm{.}4\mathrm{.}2$: Visualizing the Prim$-$Jarnik algorithm $($continued in figure below$).$

gure $15\mathrm{.}4\mathrm{.}3$: Visualizing the Prim$-$Jarn$$k algorithm $($continued from figure above$).$