chore: Move to the mono repo layout

frontends/concrete-python/docs/dev/fusing.md

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+# Fusing
+
+Fusing is the act of combining multiple nodes into a single node, which is converted to a table lookup.
+
+## How is it done?
+
+Code related to fusing is in the `concrete/numpy/compilation/utils.py` file. Fusing can be performed using the `fuse` function.
+
+Within `fuse`:
+
+1. We loop until there are no more subgraphs to fuse.
+2. <mark style="background-color:yellow;">Within each iteration:</mark>
+    2.1.  We find a subgraph to fuse.
+
+    2.2.  We search for a terminal node that is appropriate for fusing.
+
+    2.3. We crawl backwards to find the closest integer nodes to this node.
+
+    2.4.  If there is a single node as such, we return the subgraph from this node to the terminal node.
+
+    2.5. Otherwise, we try to find the lowest common ancestor (lca) of this list of nodes.
+
+    2.6. If an lca doesn't exist, we say this particular terminal node is not fusable, and we go back to search for another subgraph.
+
+    2.7. Otherwise, we use this lca as the input of the subgraph and continue with `subgraph` node creation below.
+
+    2.8.  We convert the subgraph into a `subgraph` node by checking fusability status of the nodes of the subgraph in this step.
+
+    2.10. We substitute the `subgraph` node to the original graph.
+
+## Limitations
+
+With the current implementation, we cannot fuse subgraphs that depend on multiple encrypted values where those values doesn't have a common lca (e.g., `np.round(np.sin(x) + np.cos(y))`).
+
+{% hint style="info" %}
+[Kolmogorov–Arnold representation theorem](https://en.wikipedia.org/wiki/Kolmogorov%E2%80%93Arnold\_representation\_theorem) states that every multivariate continuous function can be represented as a superposition of continuous functions of one variable. Therefore, the case above could be handled in future versions of **Concrete-Numpy**.
+{% endhint %}