import torch


def calc_planar(a_coord: torch.Tensor, b_coord: torch.Tensor,
                c_coord: torch.Tensor) -> torch.Tensor:
    """
    Calculate a planar angle between tensors of coords
    """
    v1 = a_coord - b_coord
    v2 = c_coord - b_coord

    a = (v1 * v2).sum(-1)
    b = v1.norm(dim=-1) * v2.norm(dim=-1)

    planar = torch.acos(a / b)

    return planar