Formula (2) in Exercise 7.1 incorrect
In the formula, the sum goes from 1 to |C| on j and from 1 to j-1 on i. The expression does not depend on C, only on |C|, which is obviously wrong. It should be a sum over elements from C instead:
\sum_{j \in C} \sum_{i \in C, i < j} x_{ij} \leq |C|-1
I would also emphasize that this should hold for all C satisfying the conditions:
\forall C \subset V : 3 \leq |C| \leq n-1