node top(r : bool; ix0, ix1 : real) returns (x0, x1 : real);
let
assert(ix0 > 0. and ix0 < 1.);
assert(ix1 > 0. and ix1 < 1.);
x0 = ix0 -> if r then 1. else pre x0 + 0.01 * pre x1;
x1 = ix1 -> if r then 1. else -0.01 * pre x0 + 0.99 * pre x1;
tel