(
..) = 0, and fully expand the first member, then every constituent whose modulus does not vanish may be equated to 0.
This enables us to interpret any equation by a general rule.
RULE. Bring all the terms to the first side, expand this in terms of all the elective symbols involved in it, and equate to 0 every constituent whose modulus does not vanish.
For the demonstration of these and many other results, I must refer to the original work. It must be noted that on p. 66[4], z has been, through mistake, substituted for
, and that the reference on p. 80[5] should be to Prop. 2.
As an example, let us take the equation
