graphical proof tree

[fred bapst]

Hello,

Does anybody know where I can find a tool that
graphically shows the "proof tree" of a Prolog
question ?

Of course a tracer like the one in GnuProlog is
what the programmer needs, but a graphical tree
would be useful for the first exercises in Prolog
(I'm teaching Prolog). 

This seems feasible through a high-level Prolog
interpreter (cf. [Sterling,Shapiro]), or by analysing
the debugger trace output...

Thanks in advance.

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