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//If you are trying to get the difference c between two quaternions a and b,
// such that a + c = b and b - c = a, the correct formula is:
DIFF = Quaternion.Inverse(FROM) * TO
TO = FROM * DIFF
FROM = TO * Quaternion.Inverse(DIFF)
// for help with applying correct rotation order:
// https://answers.unity.com/questions/810579/quaternion-multiplication-order.html