code: def default(val, d):
      return val if exists(val) else d
  
imports: import torch
  from torch import nn, einsum
  import torch.nn.functional
  from einops import rearrange, repeat
  from einops.layers.torch import Rearrange
label_desc: Use image node_id 2 for calling a global function with example usage: default(val, d) and returns: unknown