= Ideal-form correspondence for imaginary quadratic fields
{title2=$[a,b,c]\longleftrightarrow(a,(-b+\sqrt D)/2)$}
For a negative fundamental discriminant $D$, primitive positive definite integral <binary quadratic forms> of discriminant $D$, modulo proper equivalence, correspond bijectively to the <ideal class group> of $\mathbb Q(\sqrt D)$. The displayed ideal gives one conventional choice of this correspondence. <Reduced positive definite binary quadratic forms> give unique class representatives with the usual boundary sign convention, making class-number computations finite.
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