The Marschak Machina triangle is an aid to visualization of behaviors of
utility functions.
It is defined over a triangle:
Start with X={x,y,z} with x">"y">"z
S2={x in R^3: x in R^3+, Sum(i=1,3,xi=1)}
Each point in the triangle is some mixture of x,y, and z.
On this set, affine utility function should have parallel indifference lines.
A steep slope => risk averse.
In reality, peoples indifference lines seem to fan out. This is supported
by the common consequence effect and common ratio effect.