diff --git a/b2/chr.c b/b2/chr.c
index fdad4a0..1b68572 100644
--- a/b2/chr.c
+++ b/b2/chr.c
@@ -77,10 +77,26 @@ struct condition *new_condition(enum relop relop, const char *word)
 }
 
 
+static int comp(const void *a, enum relop op, const void *b, const void *user)
+{
+	return compare(user, a, op, b);
+}
+
+
+static void check_redundant(const struct field *f,
+    const struct condition *c1, const struct condition *c2)
+{
+	if (relop_implies(c1->relop, c2->relop, &c1->value, &c2->value,
+	    comp, f->fmt))
+		yywarn("redundant condition");
+}
+
+
 void field_finalize(struct field *field)
 {
-	const struct selector *sel;
+	const struct selector *sel, *s2;
 	struct condition *cond;
+	const struct condition *c2;
 
 	for (sel = field->sel; sel; sel = sel->next)
 		for (cond = sel->cond; cond; cond = cond->next)
@@ -88,6 +104,14 @@ void field_finalize(struct field *field)
 			    &cond->value))
 				yyerrorf("invalid value in selection");
 				/* @@@ indicate exact location */
+	for (sel = field->sel; sel; sel = sel->next)
+		for (cond = sel->cond; cond; cond = cond->next) {
+			for (c2 = cond->next; c2; c2 = c2->next)
+				check_redundant(field, cond, c2);
+			for (s2 = sel->next; s2; s2 = s2->next)
+				for (c2 = s2->cond; c2; c2 = c2->next)
+					check_redundant(field, cond, c2);
+		}
 }
 
 
diff --git a/b2/relop.c b/b2/relop.c
index e186c2f..ff9411b 100644
--- a/b2/relop.c
+++ b/b2/relop.c
@@ -16,6 +16,78 @@
 #include "relop.h"
 
 
+/*
+ * Operator to use for
+ *
+ * forall X: (A op B) == ((X opa A) -> (X opb B))
+ *
+ * For unlimited sets of values:
+ *
+ * opa ->  <   <=  ==  >=  >
+ * opb 
+ *  <      >=  >=  0   0   0
+ *  <=     >   >=  0   0   0
+ *  ==     >   >=  ==  <=  <
+ *  >=     0   0   0   <=  <
+ *  >      0   0   0   <=  <=
+ *
+ * For limited sets of values, we could decide also in some edge cases,
+ * but let's save such sophistication for later.
+ */
+
+
+static const enum relop implies_op[idx_n][idx_n] = {
+	[idx_lt][idx_lt] = rel_ge,
+	[idx_lt][idx_le] = rel_ge,
+
+	[idx_le][idx_lt] = rel_gt,
+	[idx_le][idx_le] = rel_ge,
+
+	[idx_eq][idx_lt] = rel_gt,
+	[idx_eq][idx_le] = rel_ge,
+	[idx_eq][idx_eq] = rel_eq,
+};
+
+
+static int relop2index(enum relop op)
+{
+	switch (op) {
+	case rel_lt:
+		return idx_lt;
+	case rel_le:
+		return idx_le;
+	case rel_eq:
+		return idx_eq;
+	case rel_ge:
+		return idx_ge;
+	case rel_gt:
+		return idx_gt;
+	default:
+		abort();
+	}
+}
+
+
+static enum relop swap_op(enum relop op)
+{
+	return idx_n-1-relop2index(op);
+}
+
+
+int relop_implies(enum relop opa, enum relop opb, const void *a, const void *b,
+    int (*cmp)(const void *a, enum relop op, const void *b, const void *user),
+    const void *user)
+{
+	if (opa <= opb)
+		return cmp(a,
+		    implies_op[relop2index(opa)][relop2index(opb)], b, user);
+	else
+		return cmp(b,
+		    swap_op(implies_op[relop2index(opb)][relop2index(opa)]),
+		    a, user);
+}
+
+
 void dump_relop(FILE *file, enum relop op)
 {
 	switch (op) {
diff --git a/b2/relop.h b/b2/relop.h
index 69facc6..adb2f50 100644
--- a/b2/relop.h
+++ b/b2/relop.h
@@ -16,15 +16,31 @@
 #include <stdio.h>
 
 
+enum relop_idx {
+	idx_lt	= 0,
+	idx_le	= 1,
+	idx_eq	= 2,
+	idx_ge	= 3,
+	idx_gt	= 4,
+	idx_n	= 5
+};
+
 enum relop {
-	rel_lt	= 1 << 0,
-	rel_le	= 1 << 1,
-	rel_eq	= 1 << 2,
-	rel_ge	= 1 << 3,
-	rel_gt	= 1 << 4,
+	rel_lt	= 1 << idx_lt,
+	rel_le	= 1 << idx_le,
+	rel_eq	= 1 << idx_eq,
+	rel_ge	= 1 << idx_ge,
+	rel_gt	= 1 << idx_gt,
 };
 
 
+/*
+ * relop_implies checks whether, for all X: (X opb A) -> (X opa B)
+ */
+
+int relop_implies(enum relop opa, enum relop opb, const void *a, const void *b,
+    int (*cmp)(const void *a, enum relop op, const void *b, const void *user),
+    const void *user);
 void dump_relop(FILE *file, enum relop op);
 
 #endif /* !RELOP_H */