+ *
+ * Use: Solves quadratic equations in a field with characteristic 2.
+ * Suppose we have an equation %$y^2 + A y + B = 0$% where
+ * %$A \ne 0$%. (If %$A = 0$% then %$y = \sqrt{B}$% and you
+ * want @gfreduce_sqrt@ instead.) Use this function to solve
+ * %$z^2 + z = B/A^2$%; then set %$y = A z$%, since
+ * %$y^2 + y = A^2 z^2 + A^2 z = A^2 (z^2 + z) = B$% as
+ * required.
+ *
+ * The two roots are %$z$% and %$z + 1$%; this function always
+ * returns the one with zero scalar coefficient.