@pimms.param<EOL><INDENT>def _properties(props):<DEDENT>
if props is None: return None<EOL>if pimms.is_itable(props): return props.persist()<EOL>elif pimms.is_map(props): return pimms.itable(props).persist()<EOL>else: raise ValueError('<STR_LIT>')<EOL>
obj._properties is an itable of property values given to the vertex-set obj; this is a
pre-processed input version of the value obj.properties.