UNIF-TRIGGER is a flag or parameter.
If this flag is non-NIL, PP* will be called to
print out information about the current unification tree
after certain events (compare UNIF-COUNTER).
Settings are:
NIL: Print nothing.
UTREE-END: Printout whenever a tree has come to an end
(either failure or success; NB UNIF-COUNTER-OUTPUT 6 or 7
will not work with this setting.)
UTREE-END1: As UTREE-END, but also gives output when quick
unification ends a tree without completing it.
UTREE-BEGIN: Printout the root node when unification is
first called.
PROPS-CHANGE: Printout whenever the properties of a node
are different from those of its parent. (Best used with
The amount of information is determined by the setting of
UNIF-COUNTER-OUTPUT. If the flag is set to NIL, this
feature will be turned off.
This flag only applies in UN88 unification.
UNIF-TRIGGER takes values of type SYMBOL.
It belongs to subjects UNIFICATION .
Its default value is NIL
Its current value is NIL.

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