		FAQ SPASS Version 2.1


Q:	How can I get an answer substitution?

A:	There are no meta predicates in SPASS available. Hence,
	this functionality is not directly supported. However it
	can be achieved by a trick. The idea is to add a new literal
	to the conjecture clause that carries the substitution and 
	will definitely be resolved away in the final step of the proof.
	For example: let x be the variable where we are 
	interested in the subsitution. Let x occur in the single
	conjecture clause C. Then extend this clause to C,P(x,a,y)
	and add the clause -P(z,u,b), where P is new, and a,b are
	constants. Furthermore make P a minimal predicate using
	a set_DomPred declaration (see the SPASS man page). This 
	will force that the final step in the proof is the one that 
	eliminates the P literal and the x will be instantiated accordingly. 
	To make this work it may be necessary to turn off certain reduction
	rules of SPASS. To get it rid of that, a trick is to extend all
	predicates in C by a further argument with the variable y and all
	other occurrences of these predicate with fresh variables.




