}
+/*
+ Do the variables in X->VARS constitute a proper
+ subset of the variables in Y->VARS?
+ */
+bool
+interaction_is_proper_subset (const struct interaction *x, const struct interaction *y)
+{
+ if (x->n_vars >= y->n_vars)
+ return false;
+
+ return interaction_is_subset (x, y);
+}
+
+/*
+ Do the variables in X->VARS constitute a
+ subset (proper or otherwise) of the variables in Y->VARS?
+ */
+bool
+interaction_is_subset (const struct interaction *x, const struct interaction *y)
+{
+ size_t i;
+ size_t j;
+ size_t n = 0;
+
+ /* By definition, a subset cannot have more members than its superset */
+ if (x->n_vars > y->n_vars)
+ return false;
+
+ /* Count the number of values which are members of both sets */
+ for (i = 0; i < x->n_vars; i++)
+ {
+ for (j = 0; j < y->n_vars; j++)
+ {
+ if (x->vars [i] == y->vars [j])
+ {
+ n++;
+ }
+ }
+ }
+
+ /* If ALL the members of X were also found in Y, then this must be a subset */
+ if (n >= x->n_vars)
+ return true;
+
+ return false;
+}
+
+
+
+
void
interaction_dump (const struct interaction *i)
{