Man pages matching name math::planepath::rationalstree in section 3pm:

Math::PlanePath::RationalsTree.3pm.en	debian 10 / libmath-planepath-perl
Math::PlanePath::RationalsTree.3pm.en	debian 11 / libmath-planepath-perl
Math::PlanePath::RationalsTree.3pm.en	debian 12 / libmath-planepath-perl