Immediately I'm reminded of the SKI calculus as an extremely minimal model for computation [0].
Edit: in fact, they even define the SKI combinators in their demonstration of Turing completeness, so I wonder how the tree calculus differs aside from being based on only a single combinator.
Edit: in fact, they even define the SKI combinators in their demonstration of Turing completeness, so I wonder how the tree calculus differs aside from being based on only a single combinator.
[0] https://en.wikipedia.org/wiki/SKI_combinator_calculus
[1] https://treecalcul.us/live/?example=demo-turing-intensional