Following the terminology of the article, CA and AC are two different stacks (C calling A vs. A calling C) so they cannot be merged. Instead, the whole flame gr

Following the terminology of the article, CA and AC are two different stacks (C calling A vs. A calling C) so they cannot be merged. Instead, the whole flame graphs form a vector space, with a dimension for each stack (with the provision that for many purposes only the positive cone makes sense). There is no meaningful operation between stacks.