Eventuellt "The Greeks bringa presenter" av Murray Leinster
Från Variety SF :
Earth has recently received an alien ship with two kinds of very helpful aliens - Greks & Aldarians, Greks the senior of the two. They're offering great new technology, & are willing to train human scientists in Grek science. They don't claim to have any expectations from humanity, apart from giving the gifts.
But Jim Hackett is noticing some anomalies in their behavior. While Aldarians are genuinely helpful, Greks' gifting feels like contempt, Grek ship is far too big compared to their declared numbers, his suspicion during his training in Grek science that they're being taught nonsense, ...
His investigations, with the help of a small band of helpers, will unravel the aliens' nasty designs as well as a weapon to beat them at their own game