Expand knowledge base, reorganize Green's functions

1 files changed, 1 insertions, 1 deletions

diff --git a/content/know/concept/time-ordered-product/index.pdc b/content/know/concept/time-ordered-product/index.pdc
index 82c9d0f..7af5acc 100644
--- a/content/know/concept/time-ordered-product/index.pdc
+++ b/content/know/concept/time-ordered-product/index.pdc
@@ -110,7 +110,7 @@ The general definition of $\mathcal{T}$ is:
 $$\begin{aligned}
     \boxed{
         \mathcal{T} \big\{ \hat{a}_1 \cdots \hat{a}_N \big\}
-        \equiv \sum_{p \in P_N}^{} (-1)^p
+        \equiv \sum_{p \in P_N}^{} (\pm 1)^p
         \bigg( \prod_{j = 1}^{N-1} \Theta\big(t_{p_j} \!-\! t_{p_{j+1}}\big) \bigg)
         \bigg( \prod_{k = 1}^N \hat{a}_{p_k}(t_{p_k}) \bigg)
     }