Issue #891: cannot safely invert `<` and `>` to `>=` and `<=` (or the

other way around). Proper fix this time.

lib/nodes.js

@@ -1461,11 +1461,7 @@
     };
     INVERSIONS = {
       '!==': '===',
-      '===': '!==',
-      '>': '<=',
-      '<=': '>',
-      '<': '>=',
-      '>=': '<'
+      '===': '!=='
     };
     Op.prototype.children = ['first', 'second'];
     Op.prototype.isUnary = function() {
@@ -1477,11 +1473,11 @@
     };
     Op.prototype.invert = function() {
       var fst, op, _ref;
-      if (op = INVERSIONS[this.operator]) {
+      if (this.isChainable() && this.first.isChainable()) {
+        this.inverted = !this.inverted;
+        return this;
+      } else if (op = INVERSIONS[this.operator]) {
         this.operator = op;
-        if (this.first.isChainable()) {
-          this.first.invert();
-        }
         return this;
       } else if (this.second) {
         return new Parens(this).invert();
@@ -1518,14 +1514,11 @@
       var code, fst, shared, _ref;
       _ref = this.first.second.cache(o), this.first.second = _ref[0], shared = _ref[1];
       fst = this.first.compile(o, LEVEL_OP);
-      if (fst.charAt(0) === '(') {
-        fst = fst.slice(1, -1);
-      }
       code = "" + fst + " && " + (shared.compile(o)) + " " + this.operator + " " + (this.second.compile(o, LEVEL_OP));
-      if (o.level < LEVEL_OP) {
+      if (o.level < LEVEL_OP && !this.inverted) {
         return code;
       } else {
-        return "(" + code + ")";
+        return "" + (this.inverted ? '!' : '') + "(" + code + ")";
       }
     };
     Op.prototype.compileExistence = function(o) {

src/nodes.coffee

@@ -1161,10 +1161,6 @@ exports.Op = class Op extends Base
   INVERSIONS =
     '!==': '==='
     '===': '!=='
-    '>':   '<='
-    '<=':  '>'
-    '<':   '>='
-    '>=':  '<'
 
   children: ['first', 'second']
 
@@ -1177,9 +1173,11 @@ exports.Op = class Op extends Base
     @operator in ['<', '>', '>=', '<=', '===', '!==']
 
   invert: ->
-    if op = INVERSIONS[@operator]
+    if @isChainable() and @first.isChainable()
+      @inverted = !@inverted
+      this
+    else if op = INVERSIONS[@operator]
       @operator = op
-      @first.invert() if @first.isChainable()
       this
     else if @second
       new Parens(this).invert()
@@ -1208,10 +1206,9 @@ exports.Op = class Op extends Base
   #     true
   compileChain: (o) ->
     [@first.second, shared] = @first.second.cache o
-    fst  = @first.compile o, LEVEL_OP
-    fst  = fst.slice 1, -1 if fst.charAt(0) is '('
+    fst = @first.compile o, LEVEL_OP
     code = "#{fst} && #{ shared.compile o } #{@operator} #{ @second.compile o, LEVEL_OP }"
-    if o.level < LEVEL_OP then code else "(#{code})"
+    if o.level < LEVEL_OP and not @inverted then code else "#{if @inverted then '!' else ''}(#{code})"
 
   compileExistence: (o) ->
     if @first.isComplex()