Linking invariants of spatial graphs

We recall definitions of linking numbers and Wu–Simon numbers for spatial graphs. We expose a `converse’ to the Conway–Gordon–Sachs theorem (i.e. description of linking functions for embeddings $K_6\to {\mathbb{R}}^3$), and some results on Wu–Simon numbers. We conjecture and discuss a generalization of the Conway–Gordon–Sachs theorem to multiple linking. The exposition is based on plane diagrams, so no knowledge of spatial geometry is required.