FIX: Lowercase pc

src/derivatives/functional-derivatives.md

@@ -204,7 +204,7 @@ Column names are unique alphanumeric values that are defined in a relevant JSON
 sidecar file. A naming convention might be to concatenate the atlas, ROI index,
 summarization method (defined below) and transformations
 (see [Time series transformations](#time-series-transformations)) using snake case.
-For example, `harvard_oxford_cortical_4_PC` could indicate ROI 4 of the Harvard-Oxford
+For example, `harvard_oxford_cortical_4_pc` could indicate ROI 4 of the Harvard-Oxford
 cortical atlas, summarized by taking the first principal component.
 
 #### Summarization methods