For a shared central mass only the true period closes the T^2 / r^3 ratio; a wrong period-square leaves it unmatched, so the candidate is rejected. The verdict is exact only for the stated periods, radii, and central mass in the ideal circular two-body model. Real orbits add eccentricity, inclination, perturbations, central-mass uncertainty, finite-body effects, and measurement uncertainty.
A wrong period-square renders as a rejected Kepler ledger. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A wrong period-square can still be displayed honestly
Try period-square 36 with radius-cubed 64.
rB3TB2=6436
Nine sixteenths does not equal one half
The checked candidate ratio is 9 over 16, so the accepted bit is 0.