sqrt and isqrt compute square roots.
sqrt returns the principal square root of number.
If the number is not a complex but is negative,
then the result is a complex.
isqrt returns the greatest integer
less than or equal to the exact positive square root of natural.
If number is a positive rational,
it is implementation-dependent
whether root is a rational or a float.
If number is a negative rational,
it is implementation-dependent
whether root is a complex rational or a complex float.
The mathematical definition of complex square root (whether or not
minus zero is supported) follows:
(sqrt x) = (exp (/ (log x) 2))
The branch cut for square root lies along the negative real axis,
continuous with quadrant II.
The range consists of the right half-plane, including the non-negative
imaginary axis and excluding the negative imaginary axis.