(<=> (3d-Point ?Pt) (Point-In ?Pt 3d-Length-Space))
(<= (Point-In $X 3d-Length-Space) (3d-Point $X))
(<=> (3d-Point ?Pt) (Point-In ?Pt 3d-Length-Space))
(=> (And (3d-Point ?P1) (3d-Point ?P2))
(<=> (Distance ?P1 ?P2 ?D)
(And (Scalar-Quantity ?D)
(Quantity.Dimension ?D Length-Dimension)
(= ?D
(Sqrt (Dot (Position ?P1 ?P2) (Position ?P1 ?P2)))))))
(Nth-Domain Position 2 3d-Point)
(Nth-Domain Position 1 3d-Point)