Ordinary reduction of an elliptic curve
= Ordinary reduction of an elliptic curve
= Ordinary reduction
{synonym}
A good reduction in characteristic $p$ is ordinary when the geometric $p$-torsion has $p$ points, equivalently its <formal group of an elliptic curve> has height one. For a <CM elliptic curve>, a good prime split in its CM field is ordinary. One of the two roots of $X^2-a_pX+p$ is a $p$-adic unit, enabling the bounded ordinary <p-adic L-function>.