I am reading the (pre-print) paper on autograd [Paszke et. al.] 4.  In that paper, both these claims are made: (1) PyTorch creates a dynamic computation graph and (2) the graph is immutable.
I cannot fully reconcile how these two statements can both be true.  Could someone please elaborate and help me understand?
I have a basic understanding of what mutability means – at least in the context of basic Python.  I also have a basic understanding that PyTorch’s graph is define-by-run, as opposed to TensorFlow etc.