code: def boolean_union(self, entities, delete_first=True, delete_other=True):
          
          out = self._boolean_operation(
              "BooleanUnion",
              [entities[0]],
              entities[1:],
              delete_first=delete_first,
              delete_other=delete_other,
          )
          # Cannot add Compound Surface yet; see
          # <https://gitlab.onelab.info/gmsh/gmsh/issues/525>.
          # if compound:
          #     self._GMSH_CODE.append("Compound Surface {{{}}};".format(out.id))
          return out
docs: Boolean union, see
          https://gmsh.info/doc/texinfo/gmsh.html#Boolean-operations input_entity
          and tool_entity are called object and tool in gmsh documentation.