+static int expr_eq(struct expr *e1, struct expr *e2);
+static struct expr *expr_eliminate_yn(struct expr *e);
+static struct expr *expr_extract_eq_and(struct expr **ep1, struct expr **ep2);
+static struct expr *expr_extract_eq_or(struct expr **ep1, struct expr **ep2);
+static void expr_extract_eq(enum expr_type type, struct expr **ep, struct expr **ep1, struct expr **ep2);
+