What is the basic integrator method of order 2 in Kahanli6()?

[wjliu]

I have read the reference of symplectic integrator Kahanli6(), that is, ‘‘Composition constants for raising the orders of unconventional schemes for ordinary differential equations’’. As far as I know, if a symmetric one-step method of order 2 is given, I can compose it to obtain higher order methods, such as Kahanli6(). So I’m curious what basic method is used, when Kahanli6() is implemented in Julia.