  Moore introduced a class of real-valued "recursive" functions by analogy with
Kleene's formulation of the standard recursive functions. While his concise
definition inspired a new line of research on analog computation, it contains
some technical inaccuracies. Focusing on his "primitive recursive" functions,
we pin down what is problematic and discuss possible attempts to remove the
ambiguity regarding the behavior of the differential recursion operator on
partial functions. It turns out that in any case the purported relation to
differentially algebraic functions, and hence to Shannon's model of analog
computation, fails.
