code: function findSymbolName (node) {
    const math = getMath()
    let n = node
  
    while (n) {
      if (math.isSymbolNode(n)) {
        return n.name
      }
      n = n.object
    }
  
    return null
  }
docs: Find the symbol name of an AssignmentNode. Recurses into the chain of
  objects to the root object.
  @param {AssignmentNode} node
  @return {string | null} Returns the name when found, else returns null.