\magnification=\magstep1


$$
F \quad = \quad - {{ G M m} \over {R^2 + A^2} }
$$

$$
E_{\rm tot} \quad = \quad - {{G M m}\over{R}} \ + \ {{1}\over{2}} m v^2 
$$


$$
\eqalign{
{\rm If \ \ } R < R_{\rm crit}, \qquad y_{i+1} &= -y_i \cr
                                \qquad v_{i+1} &= v_i \cr
}
$$

\bye
