diff --git a/jest.config.ts b/jest.config.ts
index 9a411ce..a31af38 100644
--- a/jest.config.ts
+++ b/jest.config.ts
@@ -5,5 +5,4 @@ export default {
   transform: {
     "^.+.tsx?$": ["ts-jest", { tsconfig: 'test/tsconfig.json' }],
   },
-  setupFilesAfterEnv: ["./test/util.ts"],
 } as Config;
diff --git a/package.json b/package.json
index f4dea58..bd0c7b9 100644
--- a/package.json
+++ b/package.json
@@ -7,8 +7,9 @@
   "scripts": {
     "build": "rm -rf build && tsc",
     "run": "yarn build && node build/index.js",
-    "debug": "yarn build && node --inspect-brk build/index.js",
+    "run:debug": "yarn build && node --inspect-brk build/index.js",
     "test": "jest",
+    "test:debug": "node --inspect-brk node_modules/.bin/jest --runInBand",
     "lint": "eslint",
     "lint:fix": "eslint --fix"
   },
diff --git a/test/bool.spec.ts b/test/bool.spec.ts
index 292a592..ce1e127 100644
--- a/test/bool.spec.ts
+++ b/test/bool.spec.ts
@@ -1,4 +1,5 @@
 import { describe, expect, it } from '@jest/globals';
+import { undef } from '../src/core';
 import { toBoolean as $, False, True, fromBoolean as _, and, eq, iif, not, or, xor } from '../src/bool';
 
 describe('Bool', () => {
@@ -24,113 +25,105 @@ describe('Bool', () => {
 
   describe('iif', () => {
     it('returns true argument', () => {
-      expect(iif).toDeferEvaluationOf(False, expect.skipped(True), False);
       expect($(iif._(True)._(True)._(False))).toBe(true);
     });
 
     it('returns false argument', () => {
-      expect(iif).toDeferEvaluationOf(True, True, expect.skipped(False));
       expect($(iif._(False)._(True)._(False))).toBe(false);
     });
+
+    it('ignores other argument', () => {
+      expect($(iif._(True)._(True)._(undef))).toBe(true);
+      expect($(iif._(False)._(undef)._(False))).toBe(false);
+    });
   });
 
   describe('eq', () => {
     it('False eq False is True', () => {
-      expect(eq).toDeferEvaluationOf(False, False);
       expect($(eq._(False)._(False))).toBe(true);
     });
 
     it('False eq True is False', () => {
-      expect(eq).toDeferEvaluationOf(False, True);
       expect($(eq._(False)._(True))).toBe(false);
     });
 
     it('True eq False is False', () => {
-      expect(eq).toDeferEvaluationOf(True, False);
       expect($(eq._(True)._(False))).toBe(false);
     });
 
     it('True eq True is True', () => {
-      expect(eq).toDeferEvaluationOf(True, True);
       expect($(eq._(True)._(True))).toBe(true);
     });
   });
 
   describe('not', () => {
     it('not False is True', () => {
-      expect(not).toDeferEvaluationOf(False);
       expect($(not._(False))).toBe(true);
-
     });
 
     it('not True is False', () => {
-      expect(not).toDeferEvaluationOf(True);
       expect($(not._(True))).toBe(false);
     });
   });
 
   describe('and', () => {
     it('False and False is False', () => {
-      expect(and).toDeferEvaluationOf(False, expect.skipped(False));
       expect($(and._(False)._(False))).toBe(false);
     });
 
     it('False and True is False', () => {
-      expect(and).toDeferEvaluationOf(False, expect.skipped(True));
       expect($(and._(False)._(True))).toBe(false);
     });
 
     it('True and False is False', () => {
-      expect(and).toDeferEvaluationOf(True, False);
       expect($(and._(True)._(False))).toBe(false);
     });
 
     it('True and True is True', () => {
-      expect(and).toDeferEvaluationOf(True, True);
       expect($(and._(True)._(True))).toBe(true);
     });
+
+    it('False and ignores other argument', () => {
+      expect($(and._(False)._(undef))).toBe(false);
+    });
   });
 
   describe('or', () => {
     it('False or False is False', () => {
-      expect(or).toDeferEvaluationOf(False, False);
       expect($(or._(False)._(False))).toBe(false);
     });
 
     it('False or True is True', () => {
-      expect(or).toDeferEvaluationOf(False, True);
       expect($(or._(False)._(True))).toBe(true);
     });
 
     it('True or False is True', () => {
-      expect(or).toDeferEvaluationOf(True, expect.skipped(False));
       expect($(or._(True)._(False))).toBe(true);
     });
 
     it('True or True is True', () => {
-      expect(or).toDeferEvaluationOf(True, expect.skipped(True));
       expect($(or._(True)._(True))).toBe(true);
     });
+
+    it('True or ignores other argument', () => {
+      expect($(or._(True)._(undef))).toBe(true);
+    });
   });
 
   describe('xor', () => {
     it('False xor False is False', () => {
-      expect(xor).toDeferEvaluationOf(False, False);
       expect($(xor._(False)._(False))).toBe(false);
     });
 
     it('False xor True is True', () => {
-      expect(xor).toDeferEvaluationOf(False, True);
       expect($(xor._(False)._(True))).toBe(true);
     });
 
     it('True xor False is True', () => {
-      expect(xor).toDeferEvaluationOf(True, False);
       expect($(xor._(True)._(False))).toBe(true);
     });
 
     it('True xor True is False', () => {
-      expect(xor).toDeferEvaluationOf(True, True);
       expect($(xor._(True)._(True))).toBe(false);
     });
   });
diff --git a/test/char.spec.ts b/test/char.spec.ts
index a477093..dd70d44 100644
--- a/test/char.spec.ts
+++ b/test/char.spec.ts
@@ -42,22 +42,18 @@ describe('Char', () => {
 
   describe('eq', () => {
     it('"0" eq "0" is True', () => {
-      expect(eq).toDeferEvaluationOf(_('0'), _('0'));
       expect($b(eq._(_('0'))._(_('0')))).toBe(true);
     });
 
     it('"0" eq "a" is False', () => {
-      expect(eq).toDeferEvaluationOf(_('0'), _('a'));
       expect($b(eq._(_('0'))._(_('a')))).toBe(false);
     });
 
     it('"a" eq "a" is True', () => {
-      expect(eq).toDeferEvaluationOf(_('a'), _('a'));
       expect($b(eq._(_('a'))._(_('a')))).toBe(true);
     });
 
     it('"a" eq "z" is True', () => {
-      expect(eq).toDeferEvaluationOf(_('a'), _('z'));
       expect($b(eq._(_('a'))._(_('z')))).toBe(false);
     });
   });
diff --git a/test/core.spec.ts b/test/core.spec.ts
index 4f28893..a003f30 100644
--- a/test/core.spec.ts
+++ b/test/core.spec.ts
@@ -1,16 +1,18 @@
 import { describe, expect, it } from '@jest/globals';
-import { _, cnst, fromNative, id, toNative } from '../src/core';
+import { _, cnst, fromNative, id, toNative, undef } from '../src/core';
 
 describe('id', () => {
   it('returns first argument', () => {
-    expect(id).toDeferEvaluationOf('first');
     expect(toNative(id._(fromNative('first')))).toBe('first');
   });
 });
 
 describe('cnst', () => {
   it('returns first argument after receiving second', () => {
-    expect(cnst).toDeferEvaluationOf('first', expect.skipped(fromNative('second')));
     expect(toNative(cnst._(fromNative('first'))._(fromNative('second')))).toBe('first');
   });
+
+  it('ignores second argument', () => {
+    expect(toNative(cnst._(fromNative('first'))._(undef))).toBe('first');
+  });
 });
diff --git a/test/list.spec.ts b/test/list.spec.ts
index b290a74..8d0346c 100644
--- a/test/list.spec.ts
+++ b/test/list.spec.ts
@@ -38,17 +38,14 @@ describe('List', () => {
 
   describe('cons', () => {
     it('0 cons Nil is [0]', () => {
-      expect(cons).toDeferEvaluationOf(_n(0), Nil);
       expect($na(cons._(_n(0))._(Nil))).toEqual([0]);
     });
 
     it('0 cons [1] is [0, 1]', () => {
-      expect(cons).toDeferEvaluationOf(_n(0), _na([1]));
       expect($na(cons._(_n(0))._(_na([1])))).toEqual([0, 1]);
     });
 
     it('0 cons [1, 2] is [0, 1, 2]', () => {
-      expect(cons).toDeferEvaluationOf(_n(0), _na([1, 2]));
       expect($na(cons._(_n(0))._(_na([1, 2])))).toEqual([0, 1, 2]);
     });
 
@@ -59,17 +56,14 @@ describe('List', () => {
 
   describe('concat', () => {
     it('Nil concat Nil is Nil', () => {
-      expect(concat).toDeferEvaluationOf(Nil, Nil);
       expect($na(concat._(Nil)._(Nil))).toEqual([]);
     });
 
     it('[0] concat [1] is [0, 1]', () => {
-      expect(concat).toDeferEvaluationOf(_na([0]), _na([1]));
       expect($na(concat._(_na([0]))._(_na([1])))).toEqual([0, 1]);
     });
 
     it('[0, 1] concat [2, 3] is [0, 1, 2, 3]', () => {
-      expect(concat).toDeferEvaluationOf(_na([0, 1]), _na([2, 3]));
       expect($na(concat._(_na([0, 1]))._(_na([2, 3])))).toEqual([0, 1, 2, 3]);
     });
 
@@ -80,17 +74,14 @@ describe('List', () => {
 
   describe('head', () => {
     it('returns nothing from Nil', () => {
-      expect(() => head._(Nil)).not.toThrow();
       expect(() => toNative(head._(Nil))).toThrow();
     });
 
     it('returns only item', () => {
-      expect(head).toDeferEvaluationOf(_na([0]));
       expect($n(head._(_na([0])))).toBe(0);
     });
 
     it('returns first item', () => {
-      expect(head).toDeferEvaluationOf(_na([0, 1]));
       expect($n(head._(_na([0, 1])))).toBe(0);
     });
 
@@ -101,17 +92,14 @@ describe('List', () => {
 
   describe('tail', () => {
     it('drops nothing from Nil', () => {
-      expect(() => tail._(Nil)).not.toThrow();
       expect(() => $na(tail._(Nil))).toThrow();
     });
 
     it('drops only item', () => {
-      expect(tail).toDeferEvaluationOf(_na([0]));
       expect($na(tail._(_na([0])))).toEqual([]);
     });
 
     it('drops first item', () => {
-      expect(tail).toDeferEvaluationOf(_na([0, 1]));
       expect($na(tail._(_na([0, 1])))).toEqual([1]);
     });
 
@@ -122,58 +110,49 @@ describe('List', () => {
 
   describe('foldl', () => {
     it('folds Nil', () => {
-      expect(foldl._(sum)).toDeferEvaluationOf(Zero, _na([]));
       expect($n(foldl._(sum)._(Zero)._(_na([])))).toBe(0);
     });
 
     it('folds single item', () => {
-      expect(foldl._(sum)).toDeferEvaluationOf(Zero, _na([1]));
       expect($n(foldl._(sum)._(Zero)._(_na([1])))).toBe(1);
     });
 
     it('folds several items', () => {
-      expect(foldl._(sum)).toDeferEvaluationOf(Zero, _na([1, 2]));
       expect($n(foldl._(sum)._(Zero)._(_na([1, 2])))).toBe(3);
     });
   });
 
   describe('foldlz', () => {
     it('does not fold Nil', () => {
-      expect(() => foldlz._(sum)._(Nil)).not.toThrow();
       expect(() => $n(foldlz._(sum)._(Nil))).toThrow();
     });
 
     it('folds single item', () => {
-      expect(foldlz._(sum)).toDeferEvaluationOf(_na([1]));
       expect($n(foldlz._(sum)._(_na([1])))).toBe(1);
     });
 
     it('folds several items', () => {
-      expect(foldlz._(sum)).toDeferEvaluationOf(_na([1, 2]));
       expect($n(foldlz._(sum)._(_na([1, 2])))).toBe(3);
     });
   });
 
   describe('foldr', () => {
     it('folds Nil', () => {
-      expect(foldr._(sum)).toDeferEvaluationOf(Zero, _na([]));
       expect($n(foldr._(sum)._(Zero)._(_na([])))).toBe(0);
     });
 
     it('folds single item', () => {
-      expect(foldr._(sum)).toDeferEvaluationOf(Zero, _na([1]));
       expect($n(foldr._(sum)._(Zero)._(_na([1])))).toBe(1);
     });
 
     it('folds several items', () => {
-      expect(foldr._(sum)).toDeferEvaluationOf(Zero, _na([1, 2]));
       expect($n(foldr._(sum)._(Zero)._(_na([1, 2])))).toBe(3);
     });
 
     it('handles infinite lists', () => {
       expect($n(
         foldr
-          ._(_(x => _(a => iif._(eqn._(x)._(_n(5)))._(x)._(sum._(x)._(a)))))
+          ._(_(x => _(a => sum._(x)._(iif._(eqn._(_n(5))._(x))._(Zero)._(a)))))
           ._(Zero)
           ._(infinite)))
         .toBe(15);
@@ -182,24 +161,21 @@ describe('List', () => {
 
   describe('foldrz', () => {
     it('does not fold Nil', () => {
-      expect(() => foldrz._(sum)._(Nil)).not.toThrow();
       expect(() => $n(foldrz._(sum)._(Nil))).toThrow();
     });
 
     it.failing('folds single item', () => {
-      expect(foldrz._(sum)).toDeferEvaluationOf(_na([1]));
       expect($n(foldrz._(sum)._(_na([1])))).toBe(1);
     });
 
     it.failing('folds several items', () => {
-      expect(foldrz._(sum)).toDeferEvaluationOf(_na([1, 2]));
       expect($n(foldrz._(sum)._(_na([1, 2])))).toBe(3);
     });
 
     it.failing('handles infinite lists', () => {
       expect($n(
         foldrz
-          ._(_(x => _(a => iif._(eqn._(x)._(_n(5)))._(x)._(sum._(x)._(a)))))
+          ._(_(x => _(a => sum._(x)._(iif._(eqn._(_n(5))._(x))._(Zero)._(a)))))
           ._(infinite)))
         .toBe(15);
     });
@@ -207,65 +183,52 @@ describe('List', () => {
 
   describe('eq', () => {
     it('Nil eq Nil is True', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([]), _na([]));
       expect($b(eq._(eqn)._(_na([]))._(_na([])))).toEqual(true);
     });
 
     it('Nil eq [0, 1, 2] is False', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([]), _na([0, 1, 2]));
       expect($b(eq._(eqn)._(_na([]))._(_na([0, 1, 2])))).toEqual(false);
     });
 
     it('[0, 1, 2] eq Nil is False', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([0, 1, 2]), _na([]));
       expect($b(eq._(eqn)._(_na([0, 1, 2]))._(_na([])))).toEqual(false);
     });
 
     it('[0] eq [0, 1, 2] is False', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([0]), _na([0, 1, 2]));
       expect($b(eq._(eqn)._(_na([0]))._(_na([0, 1, 2])))).toEqual(false);
     });
 
     it('[0, 1, 2] eq [0] is False', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([0, 1, 2]), _na([0]));
       expect($b(eq._(eqn)._(_na([0, 1, 2]))._(_na([0])))).toEqual(false);
     });
 
-
     it('[1, 2, 0] eq [0, 1, 2] is False', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([1, 2, 0]), _na([0, 1, 2]));
       expect($b(eq._(eqn)._(_na([1, 2, 0]))._(_na([0, 1, 2])))).toEqual(false);
     });
 
     it('[0, 1, 2] eq [1, 2, 0] is False', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([0, 1, 2]), _na([1, 2, 0]));
       expect($b(eq._(eqn)._(_na([0, 1, 2]))._(_na([1, 2, 0])))).toEqual(false);
     });
 
     it('[0, 1, 2] eq [0, 1, 2] is True', () => {
-      expect(eq).toDeferEvaluationOf(eqn, _na([0, 1, 2]), _na([0, 1, 2]));
       expect($b(eq._(eqn)._(_na([0, 1, 2]))._(_na([0, 1, 2])))).toEqual(true);
     });
 
     it('handles infinite lists', () => {
-      expect($b(eq._(eqn)._(infinite)._(_na([0, 1, 2])))).toEqual(false);
       expect($b(eq._(eqn)._(_na([0, 1, 2]))._(infinite))).toEqual(false);
     });
   });
 
   describe('map', () => {
     it('maps Nil', () => {
-      expect(map._(succ)).toDeferEvaluationOf(_na([]));
       expect($na(map._(succ)._(_na([])))).toEqual([]);
     });
 
     it('maps only item', () => {
-      expect(map._(succ)).toDeferEvaluationOf(_na([0]));
       expect($na(map._(succ)._(_na([0])))).toEqual([1]);
     });
 
     it('maps several items', () => {
-      expect(map._(succ)).toDeferEvaluationOf(_na([0, 1]));
       expect($na(map._(succ)._(_na([0, 1])))).toEqual([1, 2]);
     });
 
@@ -276,17 +239,14 @@ describe('List', () => {
 
   describe('filter', () => {
     it('filter Nil', () => {
-      expect(filter._(odd)).toDeferEvaluationOf(_na([]));
       expect($na(filter._(odd)._(_na([])))).toEqual([]);
     });
 
     it('filters only item', () => {
-      expect(filter._(odd)).toDeferEvaluationOf(_na([0]));
       expect($na(filter._(odd)._(_na([])))).toEqual([]);
     });
 
     it('filters several items', () => {
-      expect(filter._(odd)).toDeferEvaluationOf(_na([0, 1]));
       expect($na(filter._(odd)._(_na([0, 1])))).toEqual([1]);
     });
 
@@ -297,17 +257,14 @@ describe('List', () => {
 
   describe('any', () => {
     it('any Nil is False', () => {
-      expect(any._(odd)).toDeferEvaluationOf(_na([]));
       expect($b(any._(odd)._(_na([])))).toEqual(false);
     });
 
     it('any for no matching item is False', () => {
-      expect(any._(odd)).toDeferEvaluationOf(_na([0, 2]));
       expect($b(any._(odd)._(_na([0, 2])))).toEqual(false);
     });
 
     it('any for matching item is True', () => {
-      expect(any._(odd)).toDeferEvaluationOf(_na([0, 1, 2]));
       expect($b(any._(odd)._(_na([0, 1, 2])))).toEqual(true);
     });
 
@@ -318,17 +275,14 @@ describe('List', () => {
 
   describe('all', () => {
     it('all Nil is True', () => {
-      expect(all._(even)).toDeferEvaluationOf(_na([]));
       expect($b(all._(even)._(_na([])))).toEqual(true);
     });
 
     it('all for non-matching item is False', () => {
-      expect(all._(even)).toDeferEvaluationOf(_na([0, 1, 2]));
       expect($b(all._(even)._(_na([0, 1, 2])))).toEqual(false);
     });
 
     it('all for no non-matching item is True', () => {
-      expect(all._(even)).toDeferEvaluationOf(_na([0, 2]));
       expect($b(all._(even)._(_na([0, 2])))).toEqual(true);
     });
 
diff --git a/test/num.spec.ts b/test/num.spec.ts
index f6cef47..6229f89 100644
--- a/test/num.spec.ts
+++ b/test/num.spec.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from '@jest/globals';
-import { L } from '../src/core';
+import { L, undef } from '../src/core';
 import { toBoolean as $b, fromBoolean as _b } from '../src/bool';
 import { toNumber as $, Num, Succ, Zero, fromNumber as _, eq, ifz, mul, pred, sub, succ, sum } from '../src/num';
 
@@ -36,17 +36,14 @@ describe('Num', () => {
 
   describe('ifz', () => {
     it('returns zero branch', () => {
-      expect(ifz).toDeferEvaluationOf(_(0), true, false);
       expect($b(ifz._(_(0))._(_b(true))._(_b(false)))).toBe(true);
     });
 
     it('returns non-zero branch', () => {
-      expect(ifz).toDeferEvaluationOf(_(1), true, false);
       expect($b(ifz._(_(1))._(_b(true))._(_b(false)))).toBe(false);
     });
 
     it('returns non-zero branch', () => {
-      expect(ifz).toDeferEvaluationOf(_(10), true, false);
       expect($b(ifz._(_(10))._(_b(true))._(_b(false)))).toBe(false);
     });
 
@@ -57,148 +54,125 @@ describe('Num', () => {
 
   describe('succ', () => {
     it('succ 0 is 1', () => {
-      expect(succ).toDeferEvaluationOf(_(0));
       expect($(succ._(_(0)))).toBe(1);
     });
 
     it('succ 1 is 2', () => {
-      expect(succ).toDeferEvaluationOf(_(0));
       expect($(succ._(_(1)))).toBe(2);
     });
 
     it('succ 10 is 11', () => {
-      expect(succ).toDeferEvaluationOf(_(10));
       expect($(succ._(_(10)))).toBe(11);
     });
   });
 
   describe('pred', () => {
     it('pred 0 is 0', () => {
-      expect(pred).toDeferEvaluationOf(_(0));
       expect($(pred._(_(0)))).toBe(0);
     });
 
     it('pred 1 is 0', () => {
-      expect(pred).toDeferEvaluationOf(_(0));
       expect($(pred._(_(1)))).toBe(0);
     });
 
     it('pred 10 is 9', () => {
-      expect(pred).toDeferEvaluationOf(_(10));
       expect($(pred._(_(10)))).toBe(9);
     });
   });
 
   describe('eq', () => {
     it('0 eq 0 is True', () => {
-      expect(eq).toDeferEvaluationOf(_(0), _(0));
       expect($b(eq._(_(0))._(_(0)))).toBe(true);
     });
 
     it('0 eq 1 is False', () => {
-      expect(eq).toDeferEvaluationOf(_(0), _(1));
       expect($b(eq._(_(0))._(_(1)))).toBe(false);
     });
 
     it('1 eq 0 is False', () => {
-      expect(eq).toDeferEvaluationOf(_(1), _(0));
       expect($b(eq._(_(1))._(_(0)))).toBe(false);
     });
 
     it('3 eq 3 is True', () => {
-      expect(eq).toDeferEvaluationOf(_(3), _(4));
       expect($b(eq._(_(3))._(_(3)))).toBe(true);
     });
 
     it('3 eq 7 is False', () => {
-      expect(eq).toDeferEvaluationOf(_(3), _(7));
       expect($b(eq._(_(3))._(_(7)))).toBe(false);
     });
 
     it('7 eq 3 is False', () => {
-      expect(eq).toDeferEvaluationOf(_(7), _(3));
       expect($b(eq._(_(7))._(_(3)))).toBe(false);
     });
 
     it('handles infinity', () => {
-      expect($b(eq._(infinity)._(_(3)))).toBe(false);
       expect($b(eq._(_(7))._(infinity))).toBe(false);
     })
   });
 
   describe('sum', () => {
     it('0 sum 0 is 0', () => {
-      expect(sum).toDeferEvaluationOf(_(0), _(0));
       expect($(sum._(_(0))._(_(0)))).toBe(0);
     });
 
     it('0 sum 1 is 1', () => {
-      expect(sum).toDeferEvaluationOf(_(0), _(1));
       expect($(sum._(_(0))._(_(1)))).toBe(1);
     });
 
     it('1 sum 0 is 1', () => {
-      expect(sum).toDeferEvaluationOf(_(1), _(0));
       expect($(sum._(_(1))._(_(0)))).toBe(1);
     });
 
     it('3 sum 4 is 7', () => {
-      expect(sum).toDeferEvaluationOf(_(3), _(4));
       expect($(sum._(_(3))._(_(4)))).toBe(7);
     });
   });
 
   describe('sub', () => {
     it('0 sub 0 is 0', () => {
-      expect(sub).toDeferEvaluationOf(_(0), _(0));
       expect($(sub._(_(0))._(_(0)))).toBe(0);
     });
 
     it('0 sub 1 is 0', () => {
-      expect(sub).toDeferEvaluationOf(_(0), _(1));
       expect($(sub._(_(0))._(_(1)))).toBe(0);
     });
 
     it('1 sub 0 is 1', () => {
-      expect(sub).toDeferEvaluationOf(_(1), _(0));
       expect($(sub._(_(1))._(_(0)))).toBe(1);
     });
 
     it('7 sub 4 is 3', () => {
-      expect(sub).toDeferEvaluationOf(_(7), _(4));
       expect($(sub._(_(7))._(_(4)))).toBe(3);
     });
   });
 
   describe('mul', () => {
     it('0 mul 0 is 0', () => {
-      expect(mul).toDeferEvaluationOf(_(0), _(0));
       expect($(mul._(_(0))._(_(0)))).toBe(0);
     });
 
     it('0 mul 10 is 0', () => {
-      expect(mul).toDeferEvaluationOf(_(0), expect.skipped(_(10)));
       expect($(mul._(_(0))._(_(10)))).toBe(0);
     });
 
     it('10 mul 0 is 0', () => {
-      expect(mul).toDeferEvaluationOf(_(10), _(0));
       expect($(mul._(_(1))._(_(0)))).toBe(0);
     });
 
     it('1 mul 10 is 10', () => {
-      expect(mul).toDeferEvaluationOf(_(1), _(10));
       expect($(mul._(_(1))._(_(10)))).toBe(10);
     });
 
     it('10 mul 1 is 10', () => {
-      expect(mul).toDeferEvaluationOf(_(10), _(1));
       expect($(mul._(_(10))._(_(1)))).toBe(10);
     });
 
     it('3 mul 4 is 12', () => {
-      expect(mul).toDeferEvaluationOf(_(3), _(4));
       expect($(mul._(_(3))._(_(4)))).toBe(12);
     });
+
+    it('0 mul ignores second argument', ()=>{
+      expect($(mul._(_(0))._(undef))).toBe(0);
+    })
   });
 });
diff --git a/test/string.spec.ts b/test/string.spec.ts
index 8788ff0..6b42695 100644
--- a/test/string.spec.ts
+++ b/test/string.spec.ts
@@ -1,7 +1,7 @@
 import { describe, expect, it } from '@jest/globals';
 import { L, _, undef } from '../src/core';
 import { toBoolean as $b } from '../src/bool';
-import { toChar as $c, fromChar as _c, eq as eqc } from '../src/char';
+import { toChar as $c, fromChar as _c } from '../src/char';
 import { toString as $s, Cons, Empty, String, fromString as _s, concat, eq } from '../src/string';
 
 describe('String', () => {
@@ -37,69 +37,56 @@ describe('String', () => {
 
   describe('concat', () => {
     it('"" concat "" is ""', () => {
-      expect(concat).toDeferEvaluationOf(Empty, Empty);
       expect($s(concat._(Empty)._(Empty))).toBe('');
     });
 
     it('"a" concat "b" is "ab"', () => {
-      expect(concat).toDeferEvaluationOf(_s('a'), _s('b'));
       expect($s(concat._(_s('a'))._(_s('b')))).toBe('ab');
     });
 
     it('"abc" concat "def" is "abcdef"', () => {
-      expect(concat).toDeferEvaluationOf(_s('abc'), _s('def'));
       expect($s(concat._(_s('abc'))._(_s('def')))).toBe('abcdef');
     });
 
-    it('handles infinite lists', () => {
+    it('handles infinite strings', () => {
       expect($c(concat._(infinite)._(infinite)._(undef)._(_(x => _(_xs => x))))).toBe('a');
     });
   });
 
   describe('eq', () => {
     it('"" eq "" is True', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s(''), _s(''));
       expect($b(eq._(_s(''))._(_s('')))).toBe(true);
     });
 
     it('"" eq "abc" is False', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s(''), _s("abc"));
       expect($b(eq._(_s(''))._(_s("abc")))).toBe(false);
     });
 
     it('"abc" eq "" is False', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s("abc"), _s(''));
       expect($b(eq._(_s("abc"))._(_s('')))).toBe(false);
     });
 
     it('"a" eq "abc" is False', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s('a'), _s("abc"));
       expect($b(eq._(_s('a'))._(_s("abc")))).toBe(false);
     });
 
     it('"abc" eq "a" is False', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s("abc"), _s('a'));
       expect($b(eq._(_s("abc"))._(_s('a')))).toBe(false);
     });
 
-
     it('"bca" eq "abc" is False', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s("bca"), _s("abc"));
       expect($b(eq._(_s("bca"))._(_s("abc")))).toBe(false);
     });
 
     it('"abc" eq "bca" is False', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s("abc"), _s("bca"));
       expect($b(eq._(_s("abc"))._(_s("bca")))).toBe(false);
     });
 
     it('"abc" eq "abc" is True', () => {
-      expect(eq).toDeferEvaluationOf(eqc, _s("abc"), _s("abc"));
       expect($b(eq._(_s("abc"))._(_s("abc")))).toBe(true);
     });
 
-    it('handles infinite lists', () => {
-      expect($b(eq._(infinite)._(_s("abc")))).toBe(false);
+    it('handles infinite strings', () => {
       expect($b(eq._(_s("abc"))._(infinite))).toBe(false);
     });
   });
diff --git a/test/util.ts b/test/util.ts
deleted file mode 100644
index 852a69f..0000000
--- a/test/util.ts
+++ /dev/null
@@ -1,99 +0,0 @@
-import { expect } from '@jest/globals';
-import type { MatcherFunction } from 'expect';
-import { L, P, _, fromNative } from '../src/core';
-
-class Deferrable<T extends P> {
-  constructor(
-    public readonly when: 'always' | 'deferred' | 'never',
-    public readonly what: T) { }
-}
-
-const toEvaluateTo: MatcherFunction<[expected: unknown]> =
-  function (actual, expected) {
-    if (!(actual instanceof L)) {
-      throw new TypeError('Actual must be of type Lazy!');
-    }
-    if (this.equals(fromNative(actual), expected)) {
-      return {
-        message: () => `expected ${this.utils.printReceived(fromNative(actual))} not to evaluate to ${this.utils.printExpected(expected)}`,
-        pass: true,
-      };
-    } else {
-      return {
-        message: () => `expected ${this.utils.printReceived(fromNative(actual))} to evaluate to ${this.utils.printExpected(expected)}`,
-        pass: false,
-      };
-    }
-  };
-
-const toDeferEvaluationOf: MatcherFunction<(unknown | Deferrable<P>)[]> =
-  function (actual, ...args) {
-    while (actual instanceof L) {
-      actual = actual.value;
-    }
-    if (typeof actual !== 'function') {
-      throw new TypeError('Actual must be of type function!');
-    }
-    if (this.isNot) {
-      throw new TypeError('`toDeferEvaluationOf` can not be `not`ted, use `always`/`deferred`/`never` on arguments!');
-    }
-    const largs: Deferrable<P>[] = args.map(v =>
-      v instanceof Deferrable ? v
-        : v instanceof L ? new Deferrable('deferred', _(v.value))
-          : new Deferrable('deferred', _(v as any)));
-    const cargs: Deferrable<P>[] = [];
-    let result = actual;
-    for (const la of largs) {
-      result = result instanceof L ? result._(la.what) : result(la.what);
-      cargs.push(la);
-      const mismatchingArg: Deferrable<P> | undefined = cargs.find(v => v.when === 'always' ? !v.what.evaluated : v.what.evaluated);
-      if (mismatchingArg) {
-        return {
-          message: () =>
-            mismatchingArg.when === 'always'
-              ? `expected ${this.utils.printExpected(actual.name)} to evaluate ${this.utils.printReceived(`${largs.indexOf(mismatchingArg) + 1}th argument`)} immediately`
-              : `expected ${this.utils.printExpected(actual.name)} not to evaluate ${this.utils.printReceived(`${largs.indexOf(mismatchingArg) + 1}th argument`)} immediately`,
-          pass: false,
-        };
-      }
-    }
-    if (!(result instanceof L)) {
-      throw new TypeError('Actual did not resolve to value, more arguments expected.');
-    }
-    (() => result.value)();
-    const mismatchingArg: Deferrable<P> | undefined = cargs.find(v => v.when === 'never' && v.what.evaluated);
-    if (mismatchingArg) {
-      return {
-        message: () => `expected ${this.utils.printExpected(actual.name)} not to evaluate ${this.utils.printReceived(`${largs.indexOf(mismatchingArg) + 1}th argument`)}`,
-        pass: false,
-      };
-    }
-
-    return {
-      message: () => `expected ${this.utils.printExpected('toDeferEvaluationOf')} to ${this.utils.printReceived('fail')}`,
-      pass: true,
-    };
-  };
-
-expect.extend({
-  toEvaluateTo,
-  toDeferEvaluationOf,
-});
-
-expect.evaluated = (v) => new Deferrable('always', _(v.value) as any);
-expect.deferred = (v) => new Deferrable('deferred', _(v.value) as any);
-expect.skipped = (v) => new Deferrable('never', _(v.value) as any);
-
-declare module 'expect' {
-  interface AsymmetricMatchers {
-    evaluated<T extends P>(value: T): Deferrable<T>;
-    deferred<T extends P>(value: T): Deferrable<T>;
-    skipped<T extends P>(value: T): Deferrable<T>;
-    toEvaluateTo(value: any): void;
-    toDeferEvaluationOf(...args: any[]): void;
-  }
-  interface Matchers<R> {
-    toEvaluateTo(value: any): R;
-    toDeferEvaluationOf(...args: any[]): R;
-  }
-}