“Ai Vertici” is a game from "La settimana enigmistica", an Italian puzzle magazine.
The game involves filling the vertices of the following graph with numbers from 0 to 9, without repetition. The goal is to assign the numbers in such a way that, for all the triangles marked with an "x," the sum of the numbers at the three vertices is the same.
a
/ \
/ x \
b --- c
/ \ / \
/ x \ / x \
d --- e --- f
/ \ / \ / \
/ x \ / x \ / x \
g --- h --- i --- l