Let $x_{r}^{j}=1\iff$ the machine schedules job $j$ using resource $r$. My constraint says that: a resource cannot be used twice, i.e., if $x_{r}^{j}=1$, then $x_{r}^{j'}=0$ for $j'\neq j$. I write this as: $$x_{r}^{j}+x_{r}^{j'}\leq1,\forall j\neq j', \forall r.$$
Is there a better way to formulate this?