enough to see Pego theorem?''. Giulio Ascoli and Cesare Arzel\a died in 1896 and 1912,
respectively, so they could not appreciate the characterization of compact families in $ L^ 2
(\mathbb {R}^ N) $ provided by Robert L. Pego in 1985. Unlike the Italian mathematicians,
Pego employed various tools from harmonic analysis in his work (for instance the Fourier
transform or the Hausdorff-Young inequality). Our article is meant to serve as a bridge …