A feedback loop occurs when both $X$ causes $Y$ and $Y$ causes $X$ (X Leftrightarrow Y). Even if the notion of time is not explicitly modeled, this situation can arise in cross-sectional studies where data are collected over a period of time (e.g., temperature and the amount of sea ice). In the generative cause-effect problem setting, it is assumed that feedback loops are excluded. Therefore, the causal graph between $X$ and $Y$ conforms to the literature on Directed Acyclic Graphs (DAGs) restricted to two variables.