Syntax sugar up bg forms with Δ

main.tex

@@ -154,6 +154,8 @@ $\chern(E) = (r,c,d)$ of some semistabilizer $E$.
 
 	v = Chern_Char(*var("R C D", domain="real"))
 	u = Chern_Char(*var("r c d", domain="real"))
+
+	Δ = lambda v: v.Q_tilt()
 \end{sagesilent}
 
 Recall [ref] that $\chern_1^{\beta_{-}}$ has fixed bounds in terms of
@@ -185,7 +187,8 @@ and we shall be varying $\chern_0(E) = r$ to see when certain inequalities fail.
 This condition expressed in terms of $R,C,D,r,c,d$ looks as follows:
 
 \begin{sagesilent}
-	bgmlv1 = - u.Q_tilt() - (v-u).Q_tilt() + v.Q_tilt()
+	# First Bogomolov-Gieseker form expression that must be non-negative:
+	bgmlv1 = Δ(v) - Δ(u) - Δ(v-u)
 \end{sagesilent}
 
 \begin{equation}