The paper in question: M.R. Garey, R.L. Graham and D.S. Johnson. Some NP-complete geometric problems .
This paper proofs the NP-completeness of some well-known problems, such as the Steiner Tree Problem, by reducing Exact Set Cover by 3-sets to these problems.
On page 3 (labeled page 12), right above Equation (2.2), it is stated that the number of crossovers is $q < 3nt$. In the example figure (Fig. 6) on page 4 however, this is clearly not true, as the number of crossovers $q=26$, whereas $3nt=18$ (as the number of subsets $t=3$, and the size of the set to cover $3n=6$).
I would understand if $q<3(3nt)$, is this an error?
PS: even if it's an error, it would likely not change the NP-completeness proof(s). I only ask to better understand the reasoning behind them.