When a prime 
divides the elliptic
discriminant of a elliptic curve 
, two or all three roots of 
become congruent (mod 
). An elliptic curve is semistable
if, for all such primes 
, only two roots become congruent
mod 
(with more complicated definitions for
or 3).
Semistable
See also
Elliptic Curve, Elliptic DiscriminantExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Semistable." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Semistable.html