Common Mistakes

Mistake $1$: forgetting to add both edges for each clause. The clause "a OR b" needs NOT a → b AND NOT b → a. Both edges are needed. Mistake $2$: confusing node indices. Keep track of which nodes represent x and which represent NOT x.

Use a clear indexing scheme like $2i$ for $x_i$ and $2i+1$ for NOT $x_i$. Be consistent. Mistake $3$: using wrong SCC comparison. If SCC(x) > SCC(NOT x), set x to true. Make sure you understand your SCC algorithm's ordering convention.