lower becomes upper

THanks to Elias Guisado
https://stacks.math.columbia.edu/tag/014R#comment-8370

derived.tex

@@ -3248,7 +3248,7 @@ \section{Distinguished triangles in the homotopy category}
 and $Q_3^\bullet$ for the ``quotient'' complexes. In other words,
 $Q_1^n = \Ker(\pi_1^n)$, $Q_3^n = \Ker(\pi_3^n)$ and
 $Q_2^n = \Ker(\pi_2^n)$. Note that the kernels exist. Then
-$B^n = A^n \oplus Q_1^n$ and $C_n = B^n \oplus Q_3^n$, where we think of $A^n$
+$B^n = A^n \oplus Q_1^n$ and $C^n = B^n \oplus Q_3^n$, where we think of $A^n$
 as a subobject of $B^n$ and so on. This implies
 $C^n = A^n \oplus Q_1^n \oplus Q_3^n$. Note that
 $\pi_2^n = \pi_1^n \circ \pi_3^n$ is zero on both $Q_1^n$ and $Q_3^n$. Hence