Basic facts about the international language Esperanto : report published on the occasion of the International Co-operation Year 1965 /
[edited by Ivo Lapenna]
. – 2nd ed.
. – Rotterdam : Universal Esperanto Association, Reserch and Documentation Centre, 1967
. – 8 p. ; 26 cm
. – (RDC ; 7) .
Originala titolo: Bazaj faktoj pri la internacia lingvo .