= Solution
First use <relational selection> to keep the Saab cars, then a <natural join> to find their sales, and finally a <relational join> to identify the corresponding salespeople. A <relational projection> gives
$$
\boxed{\pi_{\mathsf{name}}\!\left(P\bowtie_{\mathsf{empid=salespersonid}}\left(S\bowtie\sigma_{\mathsf{make}=\text{Saab}}C\right)\right).}
$$
The <foreign keys> ensure that every sale has the referenced car and salesperson. Several qualifying sales by the same person produce just one occurrence of their name under <set semantics>. Two distinct people with the same name also yield that name only once: this is the requested <relational projection> onto names.
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