The Penrose triangle, also called the tribar (Cerf), tri-bar (Ernst 1987), impossible tribar (Pappas 1989, p. 13), or impossible triangle, is an impossible
figure published by Penrose and Penrose (1958). Penrose triangles appear prominently
in the works of Escher, who not only inspired creation of this object (Escher 1954,
Penrose and Penrose 1958), but also subsequently publicized it.
The Penrose triangle can be extended to -gonal barred objects (Cerf, Elber), including the so-called
tribox.
The figure was drawn earlier by artist Oscar Reutersvärd in 1934 during a "long lecture." For this, he was honored with a stamp by the government of Sweden in 1982 (Miller).
The Penrose triangle appears on the cover of Raghavachary (2004).
Henderson (2006) offers an impossible triangle net.