Displays the current contents of the stack. Can be used to view stack contents during stepwise execution. Nevertheless the proof tree is more convenient.

Each row of the Stack window corresponds to some atom from the tail
of a rule. The Stack window contains six columns:

Column #0 counts the stack boxes. The format is **Number.**

Column #1 contains the number of parent box. The format is **ParentNumber**.

Column #2 contains the number of the atom inside the tail of its
rule, and totality of the atoms in the tail of this rule. The format is **Number:Totality**.

Column #3 contains the number of variables in the atom and the number of variables which are in the head of the clause that has been unified with this atom. The format is **vars=Variables:Variables**.

Column #4 contains the number of the first variable which is in the atom. The variables which are in the head follow. So you know the numbers from column #3 and the number of the first variable and this means that you can calculate the numbers of all variables. The format is **(_VarNumber)**.

Column #5 contains the number of the clause that has been already unified
with this atom, and, next to this number, the numbers of the other clauses,
that can be unified with this atom, in case of backtracking. Look at **System List** window in order to find which are the clauses which correspond to these numbers. The format is **-> Current. Next. Next. Next.**.