Parallel resonance and anti-resonance

There seems to be a certain amount of uncertainty among authors as to just what is a correct definition of resonance in a parallel circuit such as shown of Fig. 1. The most common definition is that resonance is that condition which makes the total reactance, or susceptance, equal to zero. This is the condition for unity power factor. In some definitions the further condition is added that at resonance the total impedance of the circuit is a maximum. The A. I. E. E. Standardization Rules,
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for instance, say that resonance is the condition of maximum impedance obtained by varying L or C, and nothing is said about zero reactance or unity power factor. These differences in definitions have led to this investigation.