diff --git a/lib/mess/parser.js b/lib/mess/parser.js
index 975f060..70847c6 100644
--- a/lib/mess/parser.js
+++ b/lib/mess/parser.js
@@ -769,7 +769,7 @@ mess.Parser = function Parser(env) {
             selector: function() {
                 var a, attachment;
                 var e, elements = [];
-                var f, filters = [];
+                var f, filters = {};
                 var z, zoom = tree.Zoom.all;
                 var segments = 0, conditions = 0;
 
@@ -786,7 +786,7 @@ mess.Parser = function Parser(env) {
                         zoom &= z;
                         conditions++;
                     } else if (f) {
-                        filters.push(f);
+                        filters[f.id] = f;
                         conditions++;
                     } else if (attachment) {
                         throw errorMessage('Encountered second attachment name', i - 1);
diff --git a/lib/mess/renderer.js b/lib/mess/renderer.js
index 5becf0a..283bc35 100644
--- a/lib/mess/renderer.js
+++ b/lib/mess/renderer.js
@@ -285,19 +285,19 @@ mess.Renderer = function Renderer(env) {
             var result = [];
             outer: for (var i = 0; i < selectors.length; i++) {
                 for (var j = result.length - 1; j >= 0; j--) {
-                    if (result[j].includesFiltersOf(selectors[i])) {
+                    if (result[j].isIncludedIn(selectors[i])) {
                         if (result[j].includesZoomOf(selectors[i])) {
                             // The existing selector is already more generic than
                             // this one.
                             continue outer;
                         }
-                        if (selectors[i].includesFiltersOf(result[j])) {
+                        if (selectors[i].isIncludedIn(result[j])) {
                             // Merge selectors with the same filters but different zooms.
                             result[j].zoom |= selectors[i].zoom;
                             continue outer;
                         }
                     }
-                    if (selectors[i].includesFiltersOf(result[j]) &&
+                    if (selectors[i].isIncludedIn(result[j]) &&
                         selectors[i].includesZoomOf(result[j])) {
                         // This selector is more generic; remove the old one.
                         result.splice(j, 1);
@@ -335,7 +335,6 @@ mess.Renderer = function Renderer(env) {
             //
             // if (shortcut) return definitions;
 
-
             for (var i = 0; i < definitions.length; i++) {
                 if (!definitions[i].selector.sound()) {
                     continue;
@@ -345,7 +344,6 @@ mess.Renderer = function Renderer(env) {
                 var selectors = [ definitions[i].selector.clone() ];
 
                 // Add the negated previous selectors.
-
                 var mergeTime = +new Date;
                 for (var j = 0; j < previousSelectors.length; j++) {
                     for (var k = selectors.length - 1; k >= 0; k--) {
@@ -372,6 +370,7 @@ mess.Renderer = function Renderer(env) {
                 for (var k = 0; k < selectors.length; k++) {
                     var rule = definitions[i].clone();
                     rule.selector = selectors[k];
+                    tree.Filter.simplify(rule.selector.filters);
                     rules.push(rule);
                 }
             }
@@ -429,7 +428,7 @@ mess.Renderer = function Renderer(env) {
                 output = [];
 
             if (err) {
-                callback(err) 
+                callback(err)
                 return;
             }
 
@@ -500,7 +499,7 @@ mess.Renderer = function Renderer(env) {
                         + '+nadgrids=@null +no_defs">\n');
 
                     output.push('</Map>');
-                    
+
                     env.errors.map(function(e) {
                         if (!e.line && e.index && e.filename) {
                             var matches = stylesheets.filter(function(s) {
diff --git a/lib/mess/tree/filter.js b/lib/mess/tree/filter.js
index 0135523..bb4f9e8 100644
--- a/lib/mess/tree/filter.js
+++ b/lib/mess/tree/filter.js
@@ -5,6 +5,7 @@ tree.Filter = function Filter(key, op, val, index) {
     this.op = op;
     this.val = val;
     this.index = index;
+    this.id = this.key + this.op + this.val;
 };
 
 tree.Filter.prototype.toXML = function(env) {
@@ -21,7 +22,7 @@ tree.Filter.prototype.toXML = function(env) {
 };
 
 tree.Filter.prototype.toString = function() {
-    return '[' + this.key + ' ' + this.op.value + ' ' + this.val + ']';
+    return '[' + this.id + ']';
 };
 
 /**
@@ -60,16 +61,107 @@ tree.Filter.prototype.clone = function() {
 };
 
 tree.Filter.sound = function(filters) {
-    // shortcut for single-filter filters
-    if (filters.length == 1) return true;
-    for (var i = 0; i < filters.length; i++) {
-        for (var j = i + 1; j < filters.length; j++) {
-            if (filters[i].conflictsWith(filters[j])) {
-                return false;
-            }
+    // Shortcut for single-filter filters.
+    if (Object.keys(filters).length == 1) return true;
+
+    var byKey = {};
+    var filter, key, value;
+
+    for (var id in filters) {
+        filter = filters[id];
+        key = filters[id].key;
+        value = filters[id].val.toString();
+
+        if (!(key in byKey)) {
+            byKey[key] = {};
+        }
+
+        switch (filter.op.value) {
+            case '=':
+                if ('='  in byKey[key] && byKey[key]['='] != value) return false;
+                if ('!=' in byKey[key] && byKey[key]['!='].indexOf(value) >= 0) return false;
+                if ('>'  in byKey[key] && byKey[key]['>'] <= value) return false;
+                if ('<'  in byKey[key] && byKey[key]['<'] >= value) return false;
+                if ('>=' in byKey[key] && byKey[key]['>='] < value) return false;
+                if ('<=' in byKey[key] && byKey[key]['<='] > value) return false;
+                byKey[key]['='] = value;
+                break;
+
+            case '!=':
+                if ('='  in byKey[key] && byKey[key]['='] == value) return false;
+                if (!('!=' in byKey[key])) byKey[key]['!='] = [];
+                byKey[key]['!='].push(value);
+                break;
+
+            case '>':
+                if ('='  in byKey[key] && byKey[key]['='] <= value) return false;
+                if ('<'  in byKey[key] && byKey[key]['<'] <= value) return false;
+                if ('<=' in byKey[key] && byKey[key]['<='] <= value) return false;
+                byKey[key]['>'] = value;
+                break;
+
+            case '<':
+                if ('='  in byKey[key] && byKey[key]['='] >= value) return false;
+                if ('>'  in byKey[key] && byKey[key]['<'] >= value) return false;
+                if ('>=' in byKey[key] && byKey[key]['<='] >= value) return false;
+                byKey[key]['<'] = value;
+                break;
+
+            case '>=':
+                if ('='  in byKey[key] && byKey[key]['='] < value) return false;
+                if ('<'  in byKey[key] && byKey[key]['<'] < value) return false;
+                if ('<=' in byKey[key] && byKey[key]['<='] < value) return false;
+                byKey[key]['>='] = value;
+                break;
+
+            case '<=':
+                if ('='  in byKey[key] && byKey[key]['='] > value) return false;
+                if ('<'  in byKey[key] && byKey[key]['<'] > value) return false;
+                if ('<=' in byKey[key] && byKey[key]['<='] > value) return false;
+                byKey[key]['<='] = value;
+                break;
         }
     }
+    delete byKey;
     return true;
 };
 
+tree.Filter.simplify = function(filters) {
+    // Shortcut for single-filter filters.
+    if (Object.keys(filters).length == 1) return true;
+
+    var byKey = {};
+    var filter, key, value;
+
+    for (var id in filters) {
+        filter = filters[id];
+        key = filters[id].key;
+        value = filters[id].val.toString();
+
+        switch (filter.op.value) {
+            case '=':
+                if (byKey[key]) {
+                    for (var i in byKey[key]) {
+                        delete filters[i];
+                    }
+                }
+                byKey[key] = '=';
+                break;
+
+
+            case '!=':
+                if (byKey[key] == '=') {
+                    delete filters[id];
+                } else {
+                    if (!byKey[key]) byKey[key] = {};
+                    byKey[key][id] = true;
+                }
+                break;
+
+            // TODO: >, <, >=, <=
+        }
+    }
+    delete byKey;
+};
+
 })(require('mess/tree'));
diff --git a/lib/mess/tree/selector.js b/lib/mess/tree/selector.js
index a3251d4..4b8b411 100644
--- a/lib/mess/tree/selector.js
+++ b/lib/mess/tree/selector.js
@@ -5,7 +5,7 @@ var assert = require('assert');
 tree.Selector = function Selector(elements, filters, zoom, attachment, conditions, index) {
     this.elements = elements || [];
     this.attachment = attachment || '__default__';
-    this.filters = filters || [];
+    this.filters = filters;
     this.zoom = zoom;
     this.conditions = conditions;
     this.index = index;
@@ -19,23 +19,32 @@ tree.Selector.prototype.debug = function() {
 
     var str = "[" + num + "] " + this.elements.join('');
     if (this.attachment !== '__default__') str += '::' + this.attachment;
-    str += ': ';
-    str += tree.Zoom.toString(this.zoom);
-    str += ' ' + this.filters.join(' ');
+    str += ': Zoom[' + tree.Zoom.toString(this.zoom) + '] ';
+    for (var id in this.filters) {
+        str += this.filters[id] + ' ';
+    }
     return str;
 };
 
+tree.Selector.prototype.hash = function() {
+    var filters = Object.keys(this.filters);
+    filters.sort();
+    return (this.zoom & tree.Zoom.all) + '[' + filters.join('][') + ']';
+};
+
 tree.Selector.prototype.sound = function() {
     if (!this.zoom) return false;
-    if (this.filters.length && !tree.Filter.sound(this.filters)) return false;
-    return true;
+    return tree.Filter.sound(this.filters);
 };
 
 tree.Selector.prototype.clone = function() {
     var obj = Object.create(Object.getPrototypeOf(this));
     obj.elements = this.elements.slice();
     obj.attachment = this.attachment;
-    obj.filters = this.filters.slice();
+    obj.filters = {};
+    for (var id in this.filters) {
+        obj.filters[id] = this.filters[id];
+    }
     obj.zoom = this.zoom;
     obj.conditions = this.conditions;
     obj.index = this.index;
@@ -44,7 +53,9 @@ tree.Selector.prototype.clone = function() {
 
 tree.Selector.prototype.merge = function(obj) {
     Array.prototype.push.apply(this.elements, obj.elements);
-    Array.prototype.push.apply(this.filters, obj.filters);
+    for (var id in obj.filters) {
+        this.filters[id] = obj.filters[id];
+    }
     if (obj.attachment) this.attachment = obj.attachment;
     this.index = obj.index;
     this.zoom &= obj.zoom;
@@ -58,100 +69,67 @@ tree.Selector.prototype.merge = function(obj) {
  * it splits up the selector and creates one for each condition.
  */
 tree.Selector.prototype.mergeOrConditions = function(obj) {
-    var result = [ this ];
+    var result = {};
 
-    if (obj.filters.length) {
+    if (Object.keys(obj.filters).length) {
         if (obj.zoom != tree.Zoom.all) {
+            var clone = this.clone();
+            clone.zoom &= obj.zoom;
+            if (clone.sound()) result[clone.hash()] = clone;
+
             var negatedZoom = ~obj.zoom;
-            for (var i = 0; i < obj.filters.length; i++) {
+            for (var id in obj.filters) {
                 var selector = this.clone();
-                selector.filters.push(obj.filters[i]);
+                selector.filters[id] = obj.filters[id];
                 selector.zoom &= negatedZoom;
-                result.push(selector);
+                if (selector.sound()) {
+                    result[selector.hash()] = selector;
+                }
             }
         } else {
             // No zoom conditions, just split the selectors for each filter in obj.
-            for (var i = 1; i < obj.filters.length; i++) {
+            for (var id in obj.filters) {
                 var selector = this.clone();
-                selector.filters.push(obj.filters[i]);
-                result.push(selector);
+                selector.filters[id] = obj.filters[id];
+                if (selector.sound()) {
+                    result[selector.hash()] = selector;
+                }
             }
-            this.filters.push(obj.filters[0]);
         }
+    } else {
+        var clone = this.clone();
+        clone.zoom &= obj.zoom;
+        if (clone.sound()) result[clone.hash()] = clone;
     }
-    this.zoom &= obj.zoom;
 
-    // Simplify the resulting sound selectors.
-    result = result.filter(function(selector) {
-        if (selector.sound()) {
-            selector.simplifyFilters();
-            return true;
-        }
-    });
-
-
-    // Check selectors for soundness before we return them.
-    return result;
+    var arr = [];
+    for (var id in result) arr.push(result[id]);
+    return arr;
 };
 
-tree.Selector.prototype.simplifyFilters = function() {
-    var simplified = [];
-    var a, b;
-    filters: for (var i = 0; i < this.filters.length; i++) {
-        a = this.filters[i];
-        // Operate from the back so that we don't run into renumbering problems
-        // when deleting items from the array.
-        for (var j = simplified.length - 1; j >= 0; j--) {
-            b = simplified[j];
-            if (b.key === a.key && 
-               (b.op.value === '=' ||
-               (b.op.value == a.op.value && b.val.value == a.val.value)
-            )) {
-                continue filters;
-            }
-            else if (a.op.value === '=' &&
-                    a.key === b.key) {
-                simplified.splice(j, 1);
-            }
-        }
-        simplified.push(a);
-    }
-    this.filters = simplified;
-};
-
-tree.Selector.prototype.includesFiltersOf = function(other) {
-    // Check that this is a strict subset of other.
-    var a, b;
-    outer: for (var i = 0; i < this.filters.length; i++) {
-        a = this.filters[i];
-        for (var j = 0; j < other.filters.length; j++) {
-            b = other.filters[j];
-            if (a.key === b.key &&
-                a.op.value == b.op.value &&
-                a.val.value == b.val.value) {
-                continue outer;
-            }
-        }
-        // Couldn't find the filter in other.
-        return false;
+tree.Selector.prototype.isIncludedIn = function(other) {
+    for (var id in this.filters) {
+        if (!(id in other.filters)) return false;
     }
     return true;
 };
 
 tree.Selector.prototype.includesZoomOf = function(other) {
-    return (this.zoom | other.zoom) == this.zoom;
+    return (this.zoom | other.zoom) == other.zoom;
 };
 
 tree.Selector.prototype.negate = function() {
     var obj = Object.create(Object.getPrototypeOf(this));
     obj.elements = this.elements.slice();
     obj.attachment = this.attachment;
-    obj.index = this.index;
-
-    obj.filters = this.filters.map(function(filter) {
-        return filter.negate();
-    });
+    obj.filters = {};
+    for (var id in this.filters) {
+        var negated = this.filters[id].negate();
+        obj.filters[negated.id] = negated;
+    }
     obj.zoom = ~this.zoom;
+    obj.conditions = this.conditions
+    obj.index = this.index;
     return obj;
 };
 
@@ -194,9 +172,11 @@ tree.Selector.prototype.layers = function(env) {
 tree.Selector.prototype.combinedFilter = function(env) {
     var conditions = tree.Zoom.toXML(this.zoom);
 
-    var filters = this.filters.map(function(filter) {
-        return '(' + filter.toXML(env).trim() + ')';
-    });
+    var filters = [];
+    for (var id in this.filters) {
+        filters.push('(' + this.filters[id].toXML(env).trim() + ')');
+    }
+
     if (filters.length) {
         conditions.push('<Filter>' + filters.join(' and ') + '</Filter>');
     }
diff --git a/test/rendering.test.js b/test/rendering.test.js
index d373b70..486f73f 100644
--- a/test/rendering.test.js
+++ b/test/rendering.test.js
@@ -44,8 +44,8 @@ helper.files('rendering', 'mml', function(file) {
 
         beforeExit(function() {
             if (!completed && renderResult) {
-                // console.warn(helper.stylize('renderer produced:', 'bold'));
-                // console.warn(renderResult);
+                console.warn(helper.stylize('renderer produced:', 'bold'));
+                console.warn(renderResult);
             }
             assert.ok(completed, 'Rendering finished.');
         });
diff --git a/test/rendering/complex_cascades.result b/test/rendering/complex_cascades.result
index e8614bd..48a0728 100644
--- a/test/rendering/complex_cascades.result
+++ b/test/rendering/complex_cascades.result
@@ -10,7 +10,12 @@
     <PolygonSymbolizer fill="#666666"/>
   </Rule>
   <Rule>
-    
+    <MinScaleDenominator>12500000</MinScaleDenominator>
+    <Filter>([NAME] = 'Canada')</Filter>
+    <PolygonSymbolizer fill="#eeeeee"/>
+  </Rule>
+  <Rule>
+    <MaxScaleDenominator>12500000</MaxScaleDenominator>
     <Filter>([NAME] = 'Canada')</Filter>
     <PolygonSymbolizer fill="#eeeeee"/>
   </Rule>
diff --git a/test/specificity.test.js b/test/specificity.test.js
index fed52d8..360f48b 100644
--- a/test/specificity.test.js
+++ b/test/specificity.test.js
@@ -10,11 +10,13 @@ var helper = require('./support/helper');
 function cleanupItem(key, value) {
     if (!key) return value.map(function(item) { return item.selector });
     else if (key === 'elements') return value.map(function(item) { return item.value; });
-    else if (key === 'filters' && !value.length) return undefined;
+    else if (key === 'filters') {
+        if (Object.keys(value).length) return Object.keys(value);
+    }
     else if (key === 'attachment' && value === '__default__') return undefined;
     else if (key === 'index') return undefined;
     else if (key === 'zoom') {
-        if (value == tree.Zoom.all) return void null;
+        if (value == tree.Zoom.all) return undefined;
         else return tree.Zoom.toString(value);
     }
     else if (key === 'op') return value.value;
diff --git a/test/specificity/demo.result b/test/specificity/demo.result
index 3b318f7..2ab94e5 100644
--- a/test/specificity/demo.result
+++ b/test/specificity/demo.result
@@ -1,8 +1,8 @@
 [
     {"elements":["#countries",".foo",".bar",".baz"]},
     {"elements":["#countries",".countries",".two"]},
-    {"elements":["#world"],"filters":[{"key":"NAME","op":"=","val":"United States"},{"key":"BLUE","op":"=","val":"red"}],"conditions":2},
-    {"elements":["#world"],"filters":[{"key":"NAME","op":"=","val":"United States"}],"conditions":1},
+    {"elements":["#world"],"filters":["NAME=United States","BLUE=red"],"conditions":2},
+    {"elements":["#world"],"filters":["NAME=United States"],"conditions":1},
     {"elements":["#countries"]},
     {"elements":["#countries"]},
     {"elements":["#world"]},
diff --git a/test/specificity/filters_and_ids.result b/test/specificity/filters_and_ids.result
index 3d2b02b..bdf4ef2 100644
--- a/test/specificity/filters_and_ids.result
+++ b/test/specificity/filters_and_ids.result
@@ -1,8 +1,8 @@
 [
-    {"elements":["#world","#countries"],"filters":[{"key":"NAME","op":"=","val":"United States"}],"conditions":1},
-    {"elements":["#world"],"filters":[{"key":"NAME","op":"=","val":"United States"}],"zoom":"......XXXXXXXXXXXXXXXXX","conditions":2},
-    {"elements":["#world"],"filters":[{"key":"NAME","op":"=","val":"United States"}],"conditions":1},
-    {"elements":["#world"],"filters":[{"key":"NAME","op":"=","val":"Canada"}],"conditions":1},
+    {"elements":["#world","#countries"],"filters":["NAME=United States"],"conditions":1},
+    {"elements":["#world"],"filters":["NAME=United States"],"zoom":"......XXXXXXXXXXXXXXXXX","conditions":2},
+    {"elements":["#world"],"filters":["NAME=United States"],"conditions":1},
+    {"elements":["#world"],"filters":["NAME=Canada"],"conditions":1},
     {"elements":[],"zoom":"......XXXXXXXXXXXXXXXXX","conditions":1},
-    {"elements":[],"filters":[{"key":"NAME","op":"=","val":"United States"}],"conditions":1}
+    {"elements":[],"filters":["NAME=United States"],"conditions":1}
 ]
\ No newline at end of file