 
 
 
?- xref:xref(queen, []).
 
nodiag / 3 calls:
        nodiag / 3
 
qdelete / 4 calls:
        qdelete / 4
 
qperm / 2 calls:
        qdelete / 4
        qperm / 2
 
queen / 2 calls:
        qperm / 2
        safe / 1
 
safe / 1 calls:
        nodiag / 3
        safe / 1
 
Yes (0.01s cpu)
?- xref:xref(queen,[builtins:on,output:daVinci]).
WARNING: module 'daVinci' does not exist, loading library...
daVinci.ecl compiled traceable 5644 bytes in 0.01 seconds
The first xref predicate call generates a textual call graph
for the queen module, while the second generates the 
daVinci graph illustrated in figure 15.1.

Figure 15.1: Call graph for queen example with built-in predicates
 
 
