A principal vertex 
of a simple polygon 
is called an ear if the diagonal ![[x_(i-1),x_(i+1)]](/images/equations/Ear/Inline3.svg)
that bridges 
lies entirely in 
. Two ears 
and 
are said to overlap if
![int[x_(i-1),x_i,x_(i+1)] intersection int[x_(j-1),x_j,x_(j+1)]!=emptyset.](/images/equations/Ear/NumberedEquation1.svg) |
The two-ears theorem states that, except for triangles, every simple polygon has at least two nonoverlapping ears.
