What does up arrow ($\uparrow$) mean in pseudocode?
The algorithms in the paper you link to are described in a notation quite similar to Pascal, a language that treats pointers in a very particular way. In Pascal, pointers are declared as references to values of specific types (a pointer to an integer can never refer to a boolean, for instance).

The upward arrow, in the example you reproduce, is a dereferencing operator. Clearly, node is a pointer to a value of a record type (not a record itself), of which p and mu are fields, so node.p has no meaning.

Check out this similar question for further clarification.