Apostrophe dictionary feature (feature 556) — divides case study labor with → Closing-parenthesis dictionary feature

Section 5's three-part methodology, input, output, and intermediate-feature analysis, is not applied evenly to one feature; the paper splits it across these two examples. The apostrophe feature carries the input analysis (Figure 4's token histogram) and the output analysis (less-than-rank-one ablation, which selectively suppresses the following 's' logit), demonstrating monosemanticity in both what activates the feature and what it causally does downstream. The closing-parenthesis feature is reserved for the third leg, intermediate/circuit analysis: sitting in the model's final layer with an unembedding that directly names closing-parenthesis tokens, its own meaning is nearly given for free, which frees the demonstration to focus entirely on tracing which upstream layer-4 features (for dates, acronyms, and other parenthesis-preceding phrases) cause it to fire. The two features thus function as complementary halves of the same argument, one showing a feature is monosemantic by input and output, the other showing dictionary features compose into traceable circuits, and neither was chosen to carry all three analyses alone.