\DOC subst_occs
\TYPE {subst_occs : int list list -> term subst -> term -> term}
\SYNOPSIS
Substitutes for particular occurrences of subterms of a given term.
\DESCRIBE
For each {{redex,residue}} in the second argument, there should be a
corresponding integer list {l_i} in the first argument that specifies
which
free occurrences of {redex_i} in the third argument should be substituted
by {residue_i}.
\FAILURE
Failure occurs if any substitution fails, or if the length of
the first argument is not equal to the length of the substitution. In
other words, every substitution pair should be accompanied by a list
specifying
when the substitution is applicable.
\EXAMPLE
{
- subst_occs [[1,3]] [Term `SUC 0` |-> Term `1`]
(Term `SUC 0 + SUC 0 = SUC(SUC 0)`);
> val it = `1 + SUC 0 = SUC 1` : term
- subst_occs [[1],[1]] [Term `SUC 0` |-> Term `1`,
Term `SUC 1` |-> Term `2`]
(Term `SUC(SUC 0) = SUC 1`);
> val it = `SUC 1 = 2` : term
- subst_occs [[1],[1]] [Term`SUC(SUC 0)` |-> Term `2`,
Term`SUC 0`
|-> Term `1`]
(Term`SUC(SUC 0) = SUC 0`);
> val it = `2 = 1` : term
}
\SEEALSO
Term.subst, Lib.|->.
\ENDDOC