code: def mut_add(self, x_prev, x_new):
      x_prev = x_prev if x_prev is not None else self.zeros()
      return self._mut_add(x_prev, x_new)
  
imports: from itertools import count
  from functools import reduce
  from .tracer import trace, primitive, toposort, Node, Box, isbox, getval
  from .util import func, subval
  import warnings
label_desc: Use image node_id 6 for calling the VSpace obj's underlying member method code with example usage: obj.mut_add(x_prev, x_new) and returns: self