Let Formula: see text be a moonshine-type vertex operator algebra generated by Virasoro vectors Formula: see text of central charge Formula: see text, where Formula: see text, such that the Virasoro vertex operator algebra generated by Formula: see text is simple, Formula: see text, and Formula: see text for distinct Formula: see text. We prove that if Formula: see text is simple, then Formula: see text is uniquely determined by its Griess algebra Formula: see text. If Formula: see text, we further prove that Formula: see text is simple. As a result, we deduce that the subalgebra Formula: see text of the parafermion vertex algebra Formula: see text generated by Formula: see text, for Formula: see text, is simple and isomorphic to Formula: see text, where Formula: see text is the root system of Formula: see text.
Feng et al. (Fri,) studied this question.