diff --git a/builtin/builtin.go b/builtin/builtin.go
index 93622fb..d462b68 100644
--- a/builtin/builtin.go
+++ b/builtin/builtin.go
@@ -36,6 +36,7 @@ var (
 		symbols.Contains:       {ast.ArgModeInput, ast.ArgModeInput},
 		symbols.Filter:         {ast.ArgModeInput},
 		symbols.Lt:             {ast.ArgModeInput, ast.ArgModeInput},
+		symbols.Ne:             {ast.ArgModeInput, ast.ArgModeInput},
 		symbols.Le:             {ast.ArgModeInput, ast.ArgModeInput},
 		symbols.Gt:             {ast.ArgModeInput, ast.ArgModeInput},
 		symbols.Ge:             {ast.ArgModeInput, ast.ArgModeInput},
@@ -271,6 +272,11 @@ func Decide(atom ast.Atom, subst *unionfind.UnionFind) (bool, []*unionfind.Union
 		}
 		return false, nil, nil
 
+	case symbols.Ne.Symbol:
+		if len(atom.Args) != 2 {
+			return false, nil, fmt.Errorf("wrong number of arguments for built-in predicate ':ne': %v", atom.Args)
+		}
+		return !atom.Args[0].Equals(atom.Args[1]), []*unionfind.UnionFind{subst}, nil
 	case symbols.Lt.Symbol:
 		if len(atom.Args) != 2 {
 			return false, nil, fmt.Errorf("wrong number of arguments for built-in predicate '<': %v", atom.Args)
diff --git a/symbols/symbols.go b/symbols/symbols.go
index 6151350..393f0f9 100644
--- a/symbols/symbols.go
+++ b/symbols/symbols.go
@@ -42,6 +42,8 @@ var (
 
 	// Lt is the less-than relation on numbers.
 	Lt = ast.PredicateSym{":lt", 2}
+	// Ne is inequality over any two evaluated constants.
+	Ne = ast.PredicateSym{":ne", 2}
 
 	// Le is the less-than-or-equal relation on numbers.
 	Le = ast.PredicateSym{":le", 2}
@@ -369,6 +371,7 @@ var (
 		Filter:      NewRelType(BoolType()),
 		// TODO: support float64
 		Lt: NewRelType(ast.NumberBound, ast.NumberBound),
+		Ne: NewRelType(ast.AnyBound, ast.AnyBound),
 		Le: NewRelType(ast.NumberBound, ast.NumberBound),
 		Gt: NewRelType(ast.NumberBound, ast.NumberBound),
 		Ge: NewRelType(ast.NumberBound, ast.NumberBound),