2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/157730Reprint of a 1989 paper including minor corrections of misprints. Added comments (11 pages) about later related papers in the literature concerning comparison of Gabriel-Zisman calculus of (right) fractions and the use of generalized morphims in the sense of Haefliger-Skandalis-Hilsum for inverting differentiable equivalences between Lie groupoids.26 pages, 3 figuresGeometric TopologyCategory Theory58H05; 18D35text