1:      1  1 CALL pred propositional:main/2-0 (det) 
mdb> echo on
Command echo enabled.
mdb> goto 10
      10:      2  2 EXIT pred propositional:a/0-0 (semidet) 
mdb> dd_wrong
a
Valid? n
c
Valid? y
Incorrect instance found:

a :-
	c.

      10:      2  2 EXIT pred propositional:a/0-0 (semidet) 
mdb> goto 21
      21:      5  2 EXIT pred propositional:b/0-0 (semidet) 
mdb> dd_wrong
b
Valid? n
f
Valid? n
i
Valid? y
Incorrect instance found:

f :-
	i.

      21:      5  2 EXIT pred propositional:b/0-0 (semidet) 
mdb> c
yes