2 belongs to a
1/( 1-2) belongs to a.
-1 belongs to a.
1/[1-(-1)] belongs to a.
1/2 belongs to a.
There are two other elements in A-1 and 1/2.
If there are only 1 x elements in a,
Then 1/( 1-x) belongs to a.
So x = 1/( 1-x)
x( 1-x)= 1
This unary quadratic equation has no real roots.
So there is no solution.
So a can't contain only one element.