  Let the Euclidean plane be simultaneously and independently endowed with a
Poisson point process and a Poisson line process, each of unit intensity.
Consider a triangle T whose vertices all belong to the point process. The
triangle is 0-pierced if no member of the line process intersects any side of
T. Our starting point is Ambartzumian's 1982 joint density for angles of T; our
exposition is elementary and raises several unanswered questions.
