trace + added by mario-goulart on Tue Mar 25 15:47:28 2014

#;1> (use trace)
#;2> (trace +)
; tracing C_plus
#;3> (+ (+ 1 2) (+ 3 4))
[0] (C_plus 1 2)
[0] C_plus -> 3 
[0] (C_plus 3 4)
[0] C_plus -> 7 
[0] (C_plus 3 7)
[0] C_plus -> 10