Ah, one additional thing I'm confused about -- what do $~$X_i$~$ and $~$x_i$~$ refer to? I thought $~$X_i$~$ referred to the node (so that SEASON would be $~$X_0$~$, {RAINING, SPRINKLER} $~$X_1$~$, {SIDEWALK} $~$X_2$~$, and {SLIPPERY} $~$X_3$~$), but then I'm not sure what lowercase $~$x_i$~$ would refer to…