first_lit
static BOOL first_lit(Positionset *fpos, Expr *e);
if (!first_lit(&r->firstpos, r->root->l)) {
(void) first_lit(fpos, e);
if (e == p->r || !first_lit(fpos, p->r))
(void) first_lit(fpos, e->l);
return (first_lit(fpos, e->l));
return ((BOOL)(first_lit(fpos, e->l) || first_lit(fpos, e->r)));
k = first_lit(fpos, e->r);
return ((BOOL)(first_lit(fpos, e->l) && k));