diff --git a/dist/helpers.js b/dist/helpers.js
index 5f92884..11ad662 100644
--- a/dist/helpers.js
+++ b/dist/helpers.js
@@ -152,6 +152,6 @@ var flatten = (function (_flatten) {
 
 exports.flatten = flatten;
 var removeSymbols = function removeSymbols(string) {
-  return string.replace(/\W/g, '');
+  return string.toString().replace(/\W/g, '');
 };
 exports.removeSymbols = removeSymbols;
\ No newline at end of file
diff --git a/npm-debug.log b/npm-debug.log
index 6de215d..fa21c44 100644
--- a/npm-debug.log
+++ b/npm-debug.log
@@ -12,21 +12,21 @@
 8 silly cache add   rawSpec: '.',
 8 silly cache add   spec: '/Users/mahdi/Documents/Workshop/equation',
 8 silly cache add   type: 'directory' }
-9 verbose addLocalDirectory /Users/mahdi/.npm/equations/1.0.0/package.tgz not in flight; packing
-10 verbose tar pack [ '/Users/mahdi/.npm/equations/1.0.0/package.tgz',
+9 verbose addLocalDirectory /Users/mahdi/.npm/equations/1.0.1/package.tgz not in flight; packing
+10 verbose tar pack [ '/Users/mahdi/.npm/equations/1.0.1/package.tgz',
 10 verbose tar pack   '/Users/mahdi/Documents/Workshop/equation' ]
-11 verbose tarball /Users/mahdi/.npm/equations/1.0.0/package.tgz
+11 verbose tarball /Users/mahdi/.npm/equations/1.0.1/package.tgz
 12 verbose folder /Users/mahdi/Documents/Workshop/equation
-13 info prepublish equations@1.0.0
-14 verbose addLocalTarball adding from inside cache /Users/mahdi/.npm/equations/1.0.0/package.tgz
-15 silly cache afterAdd equations@1.0.0
-16 verbose afterAdd /Users/mahdi/.npm/equations/1.0.0/package/package.json not in flight; writing
-17 verbose afterAdd /Users/mahdi/.npm/equations/1.0.0/package/package.json written
+13 info prepublish equations@1.0.1
+14 verbose addLocalTarball adding from inside cache /Users/mahdi/.npm/equations/1.0.1/package.tgz
+15 silly cache afterAdd equations@1.0.1
+16 verbose afterAdd /Users/mahdi/.npm/equations/1.0.1/package/package.json not in flight; writing
+17 verbose afterAdd /Users/mahdi/.npm/equations/1.0.1/package/package.json written
 18 silly publish { name: 'equations',
-18 silly publish   version: '1.0.0',
+18 silly publish   version: '1.0.1',
 18 silly publish   description: 'Equation ======== Solve math expressions or create equations for repeated and complex Math tasks.',
 18 silly publish   main: 'dist/index.js',
-18 silly publish   directories: { test: 'tests' },
+18 silly publish   directories: { test: 'dist/tests' },
 18 silly publish   scripts: { test: 'grunt test' },
 18 silly publish   keywords: [ 'Math', 'JavaScript' ],
 18 silly publish   author: { name: 'Mahdi Dibaiee' },
@@ -41,41 +41,41 @@
 18 silly publish      'grunt-eslint': '^11.0.0',
 18 silly publish      'grunt-mocha-test': '^0.12.7',
 18 silly publish      mocha: '^2.2.4' },
-18 silly publish   readme: 'Equation\n========\nSolve math expressions or create equations for repeated and complex Math tasks.\n\nTo use in browser, download [`equation.min.js`](https://raw.githubusercontent.com/mdibaiee/Equation.js/master/equation.min.js).\n\nInstall using npm:\n\n```\nnpm install equations\n```\n\n####Examples:\n\n```javascript\n// solve\nconsole.log(Equation.solve(\'4 * lg(4) ^ 3\')); // 32\n\n// equation\nlet sphereArea = Equation.equation(\'4 * PI * r^2\');\n\nconsole.log(sphereArea(5)); // 314.1592653589793\n```\n\nYou can also register your own operators and constants.\n\n```javascript\n// these options are explained below\nEquation.registerOperator(\'$\', {\n  fn: a => 1/a,\n  format: \'10\',\n  precedence: 2\n});\n\nEquation.solve(\'$2\'); // 0.5\nEquation.solve(\'$5\'); // 0.2\n\nEquation.registerConstant(\'N\', () => {\n  return Math.random() * 10 + 10\n});\n\nEquation.solve(\'N\'); // a number between 10 and 20\n```\n\nAPI\n===\n####solve(expression: String)\nTakes a math expression and evaluates it, returning the result.\n\n####equation(expression: String)\nTakes a math expression containing variables, returning a function which\nreplaces the variables with given arguments, and solves the expression.\n\n####registerOperator(key: String, options: Object)\nRegisters a new operator.\n\nOptions:\n\n#####fn\n  The function which is run on arguments and returns the result\n#####format\n  The format which specifies how arguments are placed relative to operator, this is a string in which 1 represents the operator and zeroes represent arguments.\n\n  For example `+` has the format `010` and factorial has `01`.\n#####precedence\n  Specifies the precedence of operator. The less the value, the higher the precedence, resulting in sooner execution.\n\n####registerConstant(key: String, value: Function/Number)\nRegisters a new constant. value can be a function (takes no arguments), or a constant number.\n\nThat\'s right, we have named these *constants* but they actually can change, that\'s why we can use functions to define them. An example is the `RAND` constant which calls `Math.random`.\n\nContributing\n============\nThe code is commented and I hope you don\'t have a hard time contributing,\nanyway, some tips about contributing:\n\nThe source code is in `lib` directory and is then transpiled into `dist`.\n\n#####Grunt Tasks\n######default\nTranspiles `lib` to `dist`\n######build\nTranspiles, browserifies, uglifies\n######eslint\nRuns ESLint on `lib` and `tests`\n######test\nRuns the tests\n\n---\nPlease make sure to run `grunt eslint` before commiting.\n\nIf you\'re adding something new, please add a test, too.\n\nTODO\n====\n* Equation solver\n* More tests\n',
+18 silly publish   readme: 'Equation\n========\nSolve math expressions or create equations for repeated and complex Math tasks.\n\nTo use in browser, download [`equation.min.js`](https://raw.githubusercontent.com/mdibaiee/Equation.js/master/equation.min.js).\n\nInstall using npm:\n\n```\nnpm install equations\n```\n\n####Examples:\n\n```javascript\n// solve\nconsole.log(Equation.solve(\'4 * lg(4) ^ 3\')); // 32\n\n// equation\nlet sphereArea = Equation.equation(\'4 * PI * r^2\');\n\nconsole.log(sphereArea(5)); // 314.1592653589793\n```\n\nYou can also register your own operators and constants.\n\n```javascript\n// these options are explained below\nEquation.registerOperator(\'$\', {\n  fn: a => 1/a,\n  format: \'10\',\n  precedence: 2\n});\n\nEquation.solve(\'$2\'); // 0.5\nEquation.solve(\'$5\'); // 0.2\n\nEquation.registerConstant(\'N\', () => {\n  return Math.random() * 10 + 10\n});\n\nEquation.solve(\'N\'); // a number between 10 and 20\n```\n\nFor a list of operators and constants see `[operators.js](https://github.com/mdibaiee/Equation.js/blob/master/lib/operators.js)` and `[constants.js](https://github.com/mdibaiee/Equation.js/blob/master/lib/constants.js)`.\n\nAPI\n===\n####solve(expression: String)\nTakes a math expression and evaluates it, returning the result.\n\n####equation(expression: String)\nTakes a math expression containing variables, returning a function which\nreplaces the variables with given arguments, and solves the expression.\n\n####registerOperator(key: String, options: Object)\nRegisters a new operator.\n\nOptions:\n\n#####fn\n  The function which is run on arguments and returns the result\n#####format\n  The format which specifies how arguments are placed relative to operator, this is a string in which 1 represents the operator and zeroes represent arguments.\n\n  For example `+` has the format `010` and factorial has `01`.\n#####precedence\n  Specifies the precedence of operator. The less the value, the higher the precedence, resulting in sooner execution.\n\n####registerConstant(key: String, value: Function/Number)\nRegisters a new constant. value can be a function (takes no arguments), or a constant number.\n\nThat\'s right, we have named these *constants* but they actually can change, that\'s why we can use functions to define them. An example is the `RAND` constant which calls `Math.random`.\n\nContributing\n============\nThe code is commented and I hope you don\'t have a hard time contributing,\nanyway, some tips about contributing:\n\nThe source code is in `lib` directory and is then transpiled into `dist`.\n\n#####Grunt Tasks\n######default\nTranspiles `lib` to `dist`\n######build\nTranspiles, browserifies, uglifies\n######eslint\nRuns ESLint on `lib` and `tests`\n######test\nRuns the tests\n\n---\nPlease make sure to run `grunt eslint` before commiting.\n\nIf you\'re adding something new, please add a test, too.\n',
 18 silly publish   readmeFilename: 'README.md',
-18 silly publish   gitHead: 'b08841e51b4aa34cb11edaa9a19e6983dda53bff',
-18 silly publish   _id: 'equations@1.0.0',
-18 silly publish   _shasum: '56ad9f9971b9af509e9997f5907922b792e4b2a5',
+18 silly publish   gitHead: '0970f7eb2bfcad4c474f50616cb49430b3f5fc6d',
+18 silly publish   _id: 'equations@1.0.1',
+18 silly publish   _shasum: '16a7f64cfbb8232d8babeee9419029def2aa6f44',
 18 silly publish   _from: '.' }
 19 silly mapToRegistry name equations
 20 silly mapToRegistry using default registry
 21 silly mapToRegistry registry https://registry.npmjs.org/
 22 silly mapToRegistry uri https://registry.npmjs.org/equations
 23 verbose publish registryBase https://registry.npmjs.org/
-24 silly publish uploading /Users/mahdi/.npm/equations/1.0.0/package.tgz
+24 silly publish uploading /Users/mahdi/.npm/equations/1.0.1/package.tgz
 25 verbose request uri https://registry.npmjs.org/equations
 26 verbose request sending authorization for write operation
-27 info attempt registry request try #1 at 14:49:13
+27 info attempt registry request try #1 at 17:00:50
 28 verbose request using bearer token for auth
-29 verbose request id 87deb4516c1b4c02
+29 verbose request id cee8b60a55a1f3ce
 30 http request PUT https://registry.npmjs.org/equations
 31 http 403 https://registry.npmjs.org/equations
-32 verbose headers { date: 'Tue, 21 Apr 2015 10:19:05 GMT',
+32 verbose headers { date: 'Tue, 21 Apr 2015 12:30:43 GMT',
 32 verbose headers   server: 'Apache',
 32 verbose headers   'content-type': 'application/json',
 32 verbose headers   'cache-control': 'max-age=60',
 32 verbose headers   'content-length': '95',
 32 verbose headers   'accept-ranges': 'bytes',
 32 verbose headers   via: '1.1 varnish',
-32 verbose headers   'x-served-by': 'cache-iad2126-IAD',
+32 verbose headers   'x-served-by': 'cache-fra1246-FRA',
 32 verbose headers   'x-cache': 'MISS',
 32 verbose headers   'x-cache-hits': '0',
-32 verbose headers   'x-timer': 'S1429611545.135478,VS0,VE364',
+32 verbose headers   'x-timer': 'S1429619442.117266,VS0,VE919',
 32 verbose headers   'keep-alive': 'timeout=10, max=50',
 32 verbose headers   connection: 'Keep-Alive' }
 33 verbose request invalidating /Users/mahdi/.npm/registry.npmjs.org/equations on PUT
 34 error publish Failed PUT 403
-35 verbose stack Error: "You cannot publish over the previously published version 1.0.0." : equations
+35 verbose stack Error: "You cannot publish over the previously published version 1.0.1." : equations
 35 verbose stack     at CachingRegistryClient.<anonymous> (/usr/local/lib/node_modules/npm/node_modules/npm-registry-client/lib/request.js:254:14)
 35 verbose stack     at Request._callback (/usr/local/lib/node_modules/npm/node_modules/npm-registry-client/lib/request.js:178:14)
 35 verbose stack     at Request.self.callback (/usr/local/lib/node_modules/npm/node_modules/request/request.js:344:22)
@@ -94,7 +94,7 @@
 41 error node v0.12.0
 42 error npm  v2.5.1
 43 error code E403
-44 error "You cannot publish over the previously published version 1.0.0." : equations
+44 error "You cannot publish over the previously published version 1.0.1." : equations
 45 error If you need help, you may report this error at:
 45 error     <http://github.com/npm/npm/issues>
 46 verbose exit [ 1, true ]
diff --git a/package.json b/package.json
index f603f2f..63992b5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "equations",
-  "version": "1.0.0",
+  "version": "1.0.1",
   "description": "",
   "main": "dist/index.js",
   "directories": {