Given $k\in\mathbb{Z}_{+}$, a capital Greek letter with index $k$, $\Pi_{p}^{(k)}$, always denotes a general local $p$-form with $0\leq p\leq 3$, which is of the form

(3.45)

$$\Pi_{p}^{(k)}\equiv P_{i,j_{1},\ldots,j_{p-1}}^{(k)}(x,y)(dy_{j_{1}}\wedge\ldots\wedge dy_{j_{p-1}})\wedge dx_{i}+Q_{j_{1},\ldots,j_{p}}^{(k)}(x,y)dy_{j_{1}}\wedge\ldots\wedge dy_{j_{p}},$$

where $P_{i,j_{1},\ldots,j_{p-1}}^{(k)}(x,y)$ and $Q_{j_{1},\ldots,j_{p}}^{(k)}(x,y)$ are homogeneous polynomial functions in $y$ of degree $k$ whoses coefficient functions are smooth on $U\subset P$.