Leo supports a notation for affine group literals (<x>, <y>)group,
where each of <x> and <y> can be
either an integer that specifies the coordinate,
or an indication that the coordinate should be derived
from the other coordinate so that the point is on the curve.
The latter indication is of three possible kinds:
sign high (i.e. take the value with the high sign),
sign low (i.e. take the value with the low sign),
or inferred (i.e. try sign high and sign low).
