diff --git a/id.js b/id.js
index e0e5cd4..a9c7e69 100644
--- a/id.js
+++ b/id.js
@@ -42,7 +42,7 @@ Id.prototype[fl.ap] = function(b) {
 // Traversable
 Id.prototype[fl.sequence] = function(of) {
     // the of argument is only provided for types where map might fail.
-    return this.value.map(Id[fl.of]);
+    return this.value[fl.map](Id[fl.of]);
 };
 
 // Chain
diff --git a/id_test.js b/id_test.js
index 75f2eb4..c683584 100644
--- a/id_test.js
+++ b/id_test.js
@@ -32,10 +32,10 @@ Sum.prototype[concat] = function(x) {
     return Sum(this.v + x.v);
 };
 Sum.prototype[equals] = function(x) {
-    return this.v.equals ? this.v.equals(x.v) : this.v === x.v;
+    return this.v[equals] ? this.v[equals](x.v) : this.v === x.v;
 };
 
-const equality = (x, y) => x.equals ? x.equals(y) : x === y;
+const equality = (x, y) => x[equals] ? x[equals](y) : x === y;
 const test = f => t => {
     t.ok(f("x"));
     t.done();
@@ -59,7 +59,7 @@ exports.chainRec = {
     equivalence: test((x) => {
       var predicate = a => a.length > 5
       var done = Id[of]
-      var next = a => Id[of](a.concat([x]))
+      var next = a => Id[of](a[concat]([x]))
       var initial = [x]
       return chainRec.equivalence(Id)(equality)(predicate)(done)(next)(initial)
     })
@@ -94,6 +94,9 @@ exports.monoid = {
     rightIdentity: test((x) => monoid.rightIdentity(Id[of](Sum[empty]()))(equality)(Sum[of](x)))
 };
 
+// Semigroup tests are broken otherwise for this.
+String.prototype[concat] = String.prototype.concat
+
 exports.semigroup = {
     associativity: test((x) => semigroup.associativity(Id[of])(equality)(x))
 };
diff --git a/laws/chain.js b/laws/chain.js
index 6ac8515..8044fd5 100644
--- a/laws/chain.js
+++ b/laws/chain.js
@@ -12,8 +12,8 @@ const {of, chain} = require('..');
 
 const associativity = t => eq => x => {
     const a = t[of](x)[chain](t[of])[chain](t[of]);
-    const b = t[of](x)[chain]((x) => t[of](x).chain(t[of]));
+    const b = t[of](x)[chain]((x) => t[of](x)[chain](t[of]));
     return eq(a, b);
 };
 
-module.exports = { associativity };
\ No newline at end of file
+module.exports = { associativity };
diff --git a/laws/semigroup.js b/laws/semigroup.js
index 7f2da65..1b5f3bf 100644
--- a/laws/semigroup.js
+++ b/laws/semigroup.js
@@ -21,4 +21,4 @@ const associativity = t => eq => x => {
     return eq(a, b);
 };
 
-module.exports = { associativity };
\ No newline at end of file
+module.exports = { associativity };
diff --git a/laws/traversable.js b/laws/traversable.js
index 409d48d..53177e4 100644
--- a/laws/traversable.js
+++ b/laws/traversable.js
@@ -2,7 +2,7 @@
 
 const Id = require('../id');
 const {identity} = require('fantasy-combinators');
-const {of, ap, sequence, map, equals, empty, concat} = require('..');
+const {of, ap, reduce, sequence, map, equals, empty, concat} = require('..');
 const {tagged} = require('daggy');
 
 const Compose = tagged('c');