digit/number: tau (approximately 6.2831...). The constant defined by the ratio of the circumference to the radius of all circles.

Defaults to Euclidean geometric case. Context or explicit specification of overriding this default or of a different geometry can alter its value. See also: "pai".

- ka'o'ei
- imaginary i, comma - spherical coordinates: first coordinate gives magnitude (complex modulus/radius) of the number, the second number gives the angle from the positive real axis measured counterclockwise toward the 'positive' imaginary axis (default: in the primary branch/Arg) as measured in some units (which that number should contain; the contextless default will suppose radians); the angle is not normalized.
- pi'au
- digit/number: pi (approximately 3.1416...); the constant defined by the ratio of the circumference to the diameter of all circles.