(a) Some integers do not have a square root mod *n*.

(b) When we find a square root, we have two choices (sign choice).
We must have a consistent way of choosing the sign so that we will
not make mistakes with expressions like
.
When *n* is not prime there will be more than two choices
for the square root.

Both of these problems are also problems with algebraic numbers and
will be discussed in the next part.
If we are using a field extension for the representation of *i*,
then all square roots can be represented, either by an integer
or by a multiple of the field extension.