  This note modifies the reference encoding of Turing machines in the
$\lambda$-calculus by Dal Lago and Accattoli, which is tuned for time
efficiency, as to accommodate logarithmic space. There are two main changes:
Turing machines now have *two* tapes, an input tape and a work tape, and the
input tape is encoded differently, because the reference encoding comes with a
linear space overhead for managing tapes, which is excessive for studying
logarithmic space.
