The function computes a pair $p$ of AlgebraicKernel_d_1::Bound, where $p.first$ represents the lower approximation and $p.second$ represents the upper approximation.

The pair $p$ approximates the $y$-coordinate $y$ of the AlgebraicKernel_d_2::Algebraic_real_2 value $v$ with respect to the relative precision $a$.

Postcondition

$p.first <= y$

$y <= p.second$

$(y - p.first) <= 2^{-a} |y|$

$(p.second - y) <= 2^{-a} |y|$