Hosik Chae

Thanks for the reply! As `Body` inherits both `Particle` and `RigidBody`, with updates introducing `Body.is_rigidbody` and `Body.masscenter` instead of `Particle.point` into `KanesMethod`, it looks there are no further issues that...

I am actually working on it, but there is another issue. When I try to import `Body` from [`kane.py:L6~7`](https://github.com/sympy/sympy/blob/37c7a4e7599ae60db3e12012097c175777db2254/sympy/physics/mechanics/kane.py#L6-L7), ```python ... from sympy.physics.mechanics.particle import Particle from sympy.physics.mechanics.rigidbody import RigidBody from...

Same Issue on an Intel mac (10.15.7) with `pybind11==2.9.1`. I tried to add linker options, `-undefined dynamic_lookup` as [this article](https://stackoverflow.com/questions/66026520/fatal-python-error-pymutex-lock-pyruntime-ceval-gil-mutex-failed) and [the solution commit](https://github.com/ros2/rosidl_python/commit/419fc2afe3e0b89d50dc2f6a2759d59d14270ab7) to [this issue thread](https://github.com/ros2/rosidl_python/pull/138) suggested, but...