For functions that are nested inside other functions, indentation indicates the level of nesting -- one space indent for each level of nesting. However, if the function moves the cursor away from the left margin, then the level of nesting is indicated only by the number of spaces before the word "Entering."
(trace dtr) turns trace on for function dtr. When dtr is executed, both the entrance to the function and the result are displayed.
(trace dtr rtd) turns trace on for the two functions dtr and rtd
The arguments represent functions that either are already defined, or will be defined. The trace function returns the name of the last argument whether or not it is currently defined.
Also see untrace below.
(untrace rtd) turns trace off for the given function
Also see trace above.