diff --git a/src/bool.ts b/src/bool.ts
index fb448da..8e3b148 100644
--- a/src/bool.ts
+++ b/src/bool.ts
@@ -1,30 +1,30 @@
-import { Lazy, _ } from './core';
+import { Lazy, V, _ } from './core';
 
-export type Bool = <T>(t: Lazy<T>) => (f: Lazy<T>) => Lazy<T>;
+export type Bool = Lazy<<T extends V>(t: T) => (f: T) => T>;
 
-export const True: Lazy<Bool>
-  = _(t => _ => t) as Lazy<Bool>;
+export const True: Bool
+  = _(t => _ => t) as Bool;
 
-export const False: Lazy<Bool>
+export const False: Bool
   = _(_ => f => f);
 
-export const iif: <T>(b: Lazy<Bool>) => (t: Lazy<T>) => (f: Lazy<T>) => Lazy<T>
+export const iif: <T extends V>(b: Bool) => (t: T) => (f: T) => T
   = b => t => f => b.then(b => b(t)(f));
 
-export const not: (b: Lazy<Bool>) => Lazy<Bool>
+export const not: (b: Bool) => Bool
   = b => b.then(b => b(False)(True));
 
-export const and: (l: Lazy<Bool>) => (r: Lazy<Bool>) => Lazy<Bool>
+export const and: (l: Bool) => (r: Bool) => Bool
   = l => r => l.then(l => l(r)(False));
 
-export const or: (l: Lazy<Bool>) => (r: Lazy<Bool>) => Lazy<Bool>
+export const or: (l: Bool) => (r: Bool) => Bool
   = l => r => l.then(l => l(True)(r));
 
-export const xor: (l: Lazy<Bool>) => (r: Lazy<Bool>) => Lazy<Bool>
+export const xor: (l: Bool) => (r: Bool) => Bool
   = l => r => l.then(l => l(not(r))(r));
 
-export const fromBoolean: (b: boolean) => Lazy<Bool>
+export const fromBoolean: (b: boolean) => Bool
   = b => b ? True : False;
 
-export const toBoolean: (b: Lazy<Bool>) => Lazy<boolean>
-  = b => b.then(b => b(_(true))(_(false)));
+export const toBoolean: (b: Bool) => boolean
+  = b => b.then(b => b(_(true))(_(false))).value;
diff --git a/src/core.ts b/src/core.ts
index fa98ca7..67f1815 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -13,32 +13,21 @@ export class Lazy<T> {
     return this._value = this._eval();
   }
 
-  public then<R>(f: (v: T) => Lazy<R>): Lazy<R> {
-    return new Lazy(() => f(this.value).value);
-  }
-}
-
-type Choice = <T>(t: Lazy<T>) => (f: Lazy<T>) => Lazy<T>;
-
-export class LazyChoice extends Lazy<Choice> {
-  public call<T>(l: LazyChoice): (r: LazyChoice) => LazyChoice;
-  public call<T>(l: Lazy<T>): (r: Lazy<T>) => Lazy<T>;
-  public call<T>(l: Lazy<T> | LazyChoice): (r: Lazy<T> | LazyChoice) => Lazy<T> | LazyChoice {
-    return l instanceof LazyChoice
-      ? (r: LazyChoice) => new LazyChoice(() => this.value(l)(r).value)
-      : (r: Lazy<T>) => this.then(c => c(l)(r));
+  public then<R extends V>(f: (v: T) => R): R {
+    return new Lazy(() => f(this.value).value) as R;
   }
 }
 
+export type V = Lazy<unknown>;
 
 export const _ = <T>(v: T): Lazy<T> => new Lazy(() => v);
 export const $ = <T>(v: Lazy<T>): T => v.value;
 
-export const undef: Lazy<any> = new Lazy(() => {
+export const undef: any = new Lazy(() => {
   throw new Error('undefined');
 });
 
-export const id: <T>(v: Lazy<T>) => Lazy<T>
+export const id: <T extends V>(v: T) => T
   = v => v;
-export const cnst: <T> (v: Lazy<T>) => (_: Lazy<unknown>) => Lazy<T>
+export const cnst: <T extends V> (v: T) => (_: unknown) => T
   = v => _ => v;
diff --git a/src/list.ts b/src/list.ts
index f59b200..4de96ae 100644
--- a/src/list.ts
+++ b/src/list.ts
@@ -1,50 +1,50 @@
-import { Lazy, _, cnst, id, undef } from './core';
+import { Lazy, V, _, cnst, id, undef } from './core';
 import { fromNumber, Num, toNumber } from './num';
 import { Bool, iif } from './bool';
 
-export type List<T> = <R>(z: Lazy<R>) => (f: (x: Lazy<T>) => (xs: Lazy<List<T>>) => Lazy<R>) => Lazy<R>;
+export type List<T extends V> = Lazy<<R extends V>(z: R) => (f: (x: T) => (xs: List<T>) => R) => R>;
 
-export const Nil: Lazy<List<any>>
-  = _<List<any>>(z => _ => z);
+export const Nil: List<any>
+  = _(z => _ => z) as List<any>;
 
-export const Cons: <T>(x: Lazy<T>) => (xs: Lazy<List<T>>) => Lazy<List<T>>
-  = <T>(x: Lazy<T>) => (xs: Lazy<List<T>>) => _<List<T>>(_ => f => f(x)(xs));
+export const Cons: <T extends V>(x: T) => (xs: List<T>) => List<T>
+  = <T extends V>(x: T) => (xs: List<T>) => _(_ => f => f(x)(xs)) as List<T>;
 
-export const cons: <T>(x: Lazy<T>) => (xs: Lazy<List<T>>) => Lazy<List<T>>
+export const cons: <T extends V>(x: T) => (xs: List<T>) => List<T>
   = Cons;
 
-export const head: <T>(xs: Lazy<List<T>>) => Lazy<T>
+export const head: <T extends V>(xs: List<T>) => T
   = xs => xs.then(xs => xs(undef)(cnst));
 
-export const tail: <T>(xs: Lazy<List<T>>) => Lazy<List<T>>
+export const tail: <T extends V>(xs: List<T>) => List<T>
   = xs => xs.then(xs => xs(undef)(_ => id));
 
-export const foldl: <T, R>(f: (a: Lazy<R>) => (x: Lazy<T>) => Lazy<R>) => (z: Lazy<R>) => (xs: Lazy<List<T>>) => Lazy<R>
+export const foldl: <T extends V, R extends V>(f: (a: R) => (x: T) => R) => (z: R) => (xs: List<T>) => R
   = f => z => xs => xs.then(xs => xs(z)(x => xs => foldl(f)(f(z)(x))(xs)));
 
-export const foldlz: <T>(f: (a: Lazy<T>) => (x: Lazy<T>) => Lazy<T>) => (xs: Lazy<List<T>>) => Lazy<T>
+export const foldlz: <T extends V>(f: (a: T) => (x: T) => T) => (xs: List<T>) => T
   = f => xs => xs.then(xs => xs(undef)(foldl(f)));
 
-export const foldr: <T, R>(f: (x: Lazy<T>) => (a: Lazy<R>) => Lazy<R>) => (z: Lazy<R>) => (xs: Lazy<List<T>>) => Lazy<R>
+export const foldr: <T extends V, R extends V>(f: (x: T) => (a: R) => R) => (z: R) => (xs: List<T>) => R
   = f => z => xs => xs.then(xs => xs(z)(x => xs => f(x)(foldr(f)(z)(xs))));
 
-export const foldrz: <T>(f: (x: Lazy<T>) => (a: Lazy<T>) => Lazy<T>) => (xs: Lazy<List<T>>) => Lazy<T>
+export const foldrz: <T extends V>(f: (x: T) => (a: T) => T) => (xs: List<T>) => T
   = _ => _ => undef;
 
-export const map: <T, R>(f: (x: Lazy<T>) => Lazy<R>) => (xs: Lazy<List<T>>) => Lazy<List<R>>
+export const map: <T extends V, R extends V>(f: (x: T) => R) => (xs: List<T>) => List<R>
   = f => xs => xs.then(xs => xs(Nil)(x => xs => Cons(f(x))(map(f)(xs))));
 
-export const filter: <T>(f: (x: Lazy<T>) => Lazy<Bool>) => (xs: Lazy<List<T>>) => Lazy<List<T>>
-  = <T>(f: (x: Lazy<T>) => Lazy<Bool>) => (xs: Lazy<List<T>>) => xs.then(xs => xs(Nil)(x => xs => iif<List<T>>(f(x))(Cons(x)(filter(f)(xs)))(filter(f)(xs))));
+export const filter: <T extends V>(f: (x: T) => Bool) => (xs: List<T>) => List<T>
+  = <T extends V>(f: (x: T) => Bool) => (xs: List<T>) => xs.then(xs => xs(Nil)(x => xs => iif<List<T>>(f(x))(Cons(x)(filter(f)(xs)))(filter(f)(xs))));
 
-export const fromArray: <T>(xs: T[]) => Lazy<List<T>>
-  = xs => xs.length === 0 ? Nil : new Lazy(() => Cons(_(xs[0]))(fromArray(xs.slice(1))).value);
+export const fromArray: <T extends V>(xs: T[]) => List<T>
+  = xs => xs.length === 0 ? Nil : new Lazy(() => Cons(xs[0])(fromArray(xs.slice(1))).value);
 
-export const fromNumberArray: (xs: number[]) => Lazy<List<Num>>
+export const fromNumberArray: (xs: number[]) => List<Num>
   = xs => xs.length === 0 ? Nil : new Lazy(() => Cons(fromNumber(xs[0]))(fromNumberArray(xs.slice(1))).value);
 
-export const toArray: <T>(xs: Lazy<List<T>>) => Lazy<T[]>
-  = <T>(xs: Lazy<List<T>>) => xs.then(xs => xs(_([] as T[]))(x => xs => _([x.value, ...toArray(xs).value])));
+export const toArray: <R, T extends Lazy<R>>(xs: List<T>) => R[]
+  = <R, T extends Lazy<R>>(xs: List<T>) => xs.then(xs => xs(_([] as R[]))(x => xs => _([x.value, ...toArray<R, T>(xs)]))).value;
 
-export const toNumberArray: (xs: Lazy<List<Num>>) => Lazy<number[]>
-  = xs => xs.then(xs => xs(_([] as number[]))(x => xs => _([toNumber(x).value, ...toNumberArray(xs).value])));
+export const toNumberArray: (xs: List<Num>) => number[]
+  = xs => xs.then(xs => xs(_([] as number[]))(x => xs => _([toNumber(x), ...toNumberArray(xs)]))).value;
diff --git a/src/num.ts b/src/num.ts
index 19d23ae..9799ca7 100644
--- a/src/num.ts
+++ b/src/num.ts
@@ -1,40 +1,40 @@
 import { Bool, not, True } from './bool';
-import { Lazy, _, id } from './core';
+import { Lazy, V, _, id } from './core';
 
-export type Num = <T>(z: Lazy<T>) => (n: (p: Lazy<Num>) => Lazy<T>) => Lazy<T>;
+export type Num = Lazy<<T extends V>(z: T) => (n: (p: Num) => T) => T>;
 
-export const Zero: Lazy<Num>
-  = _<Num>(z => _ => z);
+export const Zero: Num
+  = _(z => _ => z) as Num;
 
-export const Succ: (p: Lazy<Num>) => Lazy<Num>
+export const Succ: (p: Num) => Num
   = p => _(_ => n => n(p));
 
-export const ifz: <T>(n: Lazy<Num>) => (t: Lazy<T>) => (f: Lazy<T>) => Lazy<T>
+export const ifz: <T extends V>(n: Num) => (t: T) => (f: T) => T
   = n => t => f => n.then(n => n(t)(_ => f));
 
-export const succ: (n: Lazy<Num>) => Lazy<Num>
+export const succ: (n: Num) => Num
   = Succ;
 
-export const pred: (n: Lazy<Num>) => Lazy<Num>
+export const pred: (n: Num) => Num
   = n => n.then(n => n(Zero)(id));
 
-export const even: (n: Lazy<Num>) => Lazy<Bool>
+export const even: (n: Num) => Bool
   = n => n.then(n => n(True)(odd));
 
-export const odd: (n: Lazy<Num>) => Lazy<Bool>
+export const odd: (n: Num) => Bool
   = n => not(even(n));
 
-export const sum: (l: Lazy<Num>) => (r: Lazy<Num>) => Lazy<Num>
+export const sum: (l: Num) => (r: Num) => Num
   = l => r => r.then(r => r(l)(sum(Succ(l))));
 
-export const sub: (l: Lazy<Num>) => (r: Lazy<Num>) => Lazy<Num>
+export const sub: (l: Num) => (r: Num) => Num
   = l => r => r.then(r => r(l)(pr => l.then(l => l(Zero)(pl => sub(pl)(pr)))));
 
-export const mul: (l: Lazy<Num>) => (r: Lazy<Num>) => Lazy<Num>
+export const mul: (l: Num) => (r: Num) => Num
   = l => r => l.then(l => l(Zero)(pl => sum(r)(mul(pl)(r))));
 
-export const fromNumber: (n: number) => Lazy<Num>
+export const fromNumber: (n: number) => Num
   = n => !n ? Zero : new Lazy(() => Succ(fromNumber(n - 1)).value);
 
-export const toNumber: (n: Lazy<Num>) => Lazy<number>
-  = n => n.then(n => n(_(0))(p => toNumber(p).then(p => _(1 + p))));
+export const toNumber: (n: Num) => number
+  = n => n.then(n => n(_(0))(p => _(1 + toNumber(p)))).value;
diff --git a/test/bool.spec.ts b/test/bool.spec.ts
index 748286d..b1842b0 100644
--- a/test/bool.spec.ts
+++ b/test/bool.spec.ts
@@ -5,23 +5,21 @@ import { True, False, iif, and, not, or, xor, toBoolean, fromBoolean } from '../
 describe('Bool', () => {
   describe('toBoolean', () => {
     it('converts True', () => {
-      expect(toBoolean).toDeferEvaluationOf(True);
-      expect(toBoolean(True)).toEvaluateTo(true);
+      expect(toBoolean(True)).toBe(true);
     });
 
     it('converts False', () => {
-      expect(toBoolean).toDeferEvaluationOf(False);
-      expect(toBoolean(False)).toEvaluateTo(false);
+      expect(toBoolean(False)).toBe(false);
     });
   });
 
   describe('fromBoolean', () => {
     it('converts true', () => {
-      expect(toBoolean(fromBoolean(true))).toEvaluateTo(true);
+      expect(toBoolean(fromBoolean(true))).toBe(true);
     });
 
     it('converts false', () => {
-      expect(toBoolean(fromBoolean(false))).toEvaluateTo(false);
+      expect(toBoolean(fromBoolean(false))).toBe(false);
     });
   });
 
@@ -40,79 +38,79 @@ describe('Bool', () => {
   describe('not', () => {
     it('not False is True', () => {
       expect(not).toDeferEvaluationOf(False);
-      expect(toBoolean(not(False))).toEvaluateTo(true);
+      expect(toBoolean(not(False))).toBe(true);
 
     });
 
     it('not True is False', () => {
       expect(not).toDeferEvaluationOf(True);
-      expect(toBoolean(not(True))).toEvaluateTo(false);
+      expect(toBoolean(not(True))).toBe(false);
     });
   });
 
   describe('and', () => {
     it('False and False is False', () => {
       expect(and).toDeferEvaluationOf(False, expect.skipped(False));
-      expect(toBoolean(and(False)(False))).toEvaluateTo(false);
+      expect(toBoolean(and(False)(False))).toBe(false);
     });
 
     it('False and True is False', () => {
       expect(and).toDeferEvaluationOf(False, expect.skipped(True));
-      expect(toBoolean(and(False)(True))).toEvaluateTo(false);
+      expect(toBoolean(and(False)(True))).toBe(false);
     });
 
     it('True and False is False', () => {
       expect(and).toDeferEvaluationOf(True, False);
-      expect(toBoolean(and(True)(False))).toEvaluateTo(false);
+      expect(toBoolean(and(True)(False))).toBe(false);
     });
 
     it('True and True is True', () => {
       expect(and).toDeferEvaluationOf(True, True);
-      expect(toBoolean(and(True)(True))).toEvaluateTo(true);
+      expect(toBoolean(and(True)(True))).toBe(true);
     });
   });
 
   describe('or', () => {
     it('False or False is False', () => {
       expect(or).toDeferEvaluationOf(False, False);
-      expect(toBoolean(or(False)(False))).toEvaluateTo(false);
+      expect(toBoolean(or(False)(False))).toBe(false);
     });
 
     it('False or True is True', () => {
       expect(or).toDeferEvaluationOf(False, True);
-      expect(toBoolean(or(False)(True))).toEvaluateTo(true);
+      expect(toBoolean(or(False)(True))).toBe(true);
     });
 
     it('True or False is True', () => {
       expect(or).toDeferEvaluationOf(True, expect.skipped(False));
-      expect(toBoolean(or(True)(False))).toEvaluateTo(true);
+      expect(toBoolean(or(True)(False))).toBe(true);
     });
 
     it('True or True is True', () => {
       expect(or).toDeferEvaluationOf(True, expect.skipped(True));
-      expect(toBoolean(or(True)(True))).toEvaluateTo(true);
+      expect(toBoolean(or(True)(True))).toBe(true);
     });
   });
 
   describe('xor', () => {
     it('False xor False is False', () => {
       expect(xor).toDeferEvaluationOf(False, False);
-      expect(toBoolean(xor(False)(False))).toEvaluateTo(false);
+      expect(toBoolean(xor(False)(False))).toBe(false);
     });
 
     it('False xor True is True', () => {
       expect(xor).toDeferEvaluationOf(False, True);
-      expect(toBoolean(xor(False)(True))).toEvaluateTo(true);
+      expect(toBoolean(xor(False)(True))).toBe(true);
     });
 
     it('True xor False is True', () => {
       expect(xor).toDeferEvaluationOf(True, False);
-      expect(toBoolean(xor(True)(False))).toEvaluateTo(true);
+      expect(toBoolean(xor(True)(False))).toBe(true);
     });
 
     it('True xor True is False', () => {
       expect(xor).toDeferEvaluationOf(True, True);
-      expect(toBoolean(xor(True)(True))).toEvaluateTo(false);
+      expect(toBoolean(xor(True)(True))).toBe(false);
     });
   });
 });
diff --git a/test/list.spec.ts b/test/list.spec.ts
index 1ec5ba1..bbabea5 100644
--- a/test/list.spec.ts
+++ b/test/list.spec.ts
@@ -5,37 +5,34 @@ import { toNumber, Zero, sum, succ, Num, Succ, odd } from '../src/num';
 import { Cons, filter, foldl, foldlz, foldr, foldrz, fromArray, fromNumberArray, head, List, map, Nil, tail, toArray, toNumberArray } from '../src/list';
 
 describe('List', () => {
-  const iterate: (n: number) => Lazy<List<number>> = n => new Lazy(() => Cons(_(n))(iterate(n + 1)).value);
-  const niterate: (n: Lazy<Num>) => Lazy<List<Num>> = n => new Lazy(() => Cons(n)(niterate(Succ(n))).value);
+  const iterate: (n: number) => List<Lazy<number>> = n => new Lazy(() => Cons(_(n))(iterate(n + 1)).value);
+  const niterate: (n: Num) => List<Num> = n => new Lazy(() => Cons(n)(niterate(Succ(n))).value);
 
   describe('toArray', () => {
     it('converts []', () => {
-      expect(toArray).toDeferEvaluationOf(Nil);
-      expect(toArray(Nil)).toEvaluateTo([]);
+      expect(toArray(Nil)).toEqual([]);
     });
 
     it('converts [0]', () => {
-      expect(toArray).toDeferEvaluationOf(Cons(_(0))(Nil));
-      expect(toArray(Cons(_(0))(Nil))).toEvaluateTo([0]);
+      expect(toArray(Cons(_(0))(Nil))).toEqual([0]);
     });
 
     it('converts [0, 1]', () => {
-      expect(toArray).toDeferEvaluationOf(Cons(_(0))(Cons(_(1))(Nil)));
-      expect(toArray(Cons(_(0))(Cons(_(1))(Nil)))).toEvaluateTo([0, 1]);
+      expect(toArray(Cons(_(0))(Cons(_(1))(Nil)))).toEqual([0, 1]);
     });
   });
 
   describe('fromArray', () => {
     it('converts []', () => {
-      expect(toArray(fromArray([]))).toEvaluateTo([]);
+      expect(toArray(fromArray([]))).toEqual([]);
     });
 
     it('converts [0]', () => {
-      expect(toArray(fromArray([0]))).toEvaluateTo([0]);
+      expect(toArray(fromArray([0].map(_)))).toEqual([0]);
     });
 
     it('converts 2', () => {
-      expect(toArray(fromArray([0, 1]))).toEvaluateTo([0, 1]);
+      expect(toArray(fromArray([0, 1].map(_)))).toEqual([0, 1]);
     });
   });
 
@@ -63,17 +60,17 @@ describe('List', () => {
   describe('tail', () => {
     it('drops nothing from empty list', () => {
       expect(() => tail(Nil)).not.toThrow();
-      expect(() => $(toArray(tail(Nil)))).toThrow();
+      expect(() => toArray(tail(Nil))).toThrow();
     });
 
     it('drops only item', () => {
       expect(tail).toDeferEvaluationOf(Cons(_(0))(Nil));
-      expect(toArray(tail(Cons(_(0))(Nil)))).toEvaluateTo([]);
+      expect(toArray(tail(Cons(_(0))(Nil)))).toEqual([]);
     });
 
     it('drops first item', () => {
       expect(tail).toDeferEvaluationOf(Cons(_(0))(Cons(_(1))(Nil)));
-      expect(toArray(tail(Cons(_(0))(Cons(_(1))(Nil))))).toEvaluateTo([1]);
+      expect(toArray(tail(Cons(_(0))(Cons(_(1))(Nil))))).toEqual([1]);
     });
 
     it('handles infinite lists', () => {
@@ -84,56 +81,56 @@ describe('List', () => {
   describe('foldl', () => {
     it('folds empty list', () => {
       expect(foldl(sum)).toDeferEvaluationOf(Zero, fromNumberArray([]));
-      expect(toNumber(foldl(sum)(Zero)(fromNumberArray([])))).toEvaluateTo(0);
+      expect(toNumber(foldl(sum)(Zero)(fromNumberArray([])))).toBe(0);
     });
 
     it('folds single item', () => {
       expect(foldl(sum)).toDeferEvaluationOf(Zero, fromNumberArray([1]));
-      expect(toNumber(foldl(sum)(Zero)(fromNumberArray([1])))).toEvaluateTo(1);
+      expect(toNumber(foldl(sum)(Zero)(fromNumberArray([1])))).toBe(1);
     });
 
     it('folds several items', () => {
       expect(foldl(sum)).toDeferEvaluationOf(Zero, fromNumberArray([1, 2]));
-      expect(toNumber(foldl(sum)(Zero)(fromNumberArray([1, 2])))).toEvaluateTo(3);
+      expect(toNumber(foldl(sum)(Zero)(fromNumberArray([1, 2])))).toBe(3);
     });
   });
 
   describe('foldlz', () => {
     it('does not fold empty list', () => {
       expect(() => foldlz(sum)(Nil)).not.toThrow();
-      expect(() => $(toNumber(foldlz(sum)(Nil)))).toThrow();
+      expect(() => toNumber(foldlz(sum)(Nil))).toThrow();
     });
 
     it('folds single item', () => {
       expect(foldlz(sum)).toDeferEvaluationOf(fromNumberArray([1]));
-      expect(toNumber(foldlz(sum)(fromNumberArray([1])))).toEvaluateTo(1);
+      expect(toNumber(foldlz(sum)(fromNumberArray([1])))).toBe(1);
     });
 
     it('folds several items', () => {
       expect(foldlz(sum)).toDeferEvaluationOf(fromNumberArray([1, 2]));
-      expect(toNumber(foldlz(sum)(fromNumberArray([1, 2])))).toEvaluateTo(3);
+      expect(toNumber(foldlz(sum)(fromNumberArray([1, 2])))).toBe(3);
     });
   });
 
   describe('foldr', () => {
     it('folds empty list', () => {
       expect(foldr(sum)).toDeferEvaluationOf(Zero, fromNumberArray([]));
-      expect(toNumber(foldr(sum)(Zero)(fromNumberArray([])))).toEvaluateTo(0);
+      expect(toNumber(foldr(sum)(Zero)(fromNumberArray([])))).toBe(0);
     });
 
     it('folds single item', () => {
       expect(foldr(sum)).toDeferEvaluationOf(Zero, fromNumberArray([1]));
-      expect(toNumber(foldr(sum)(Zero)(fromNumberArray([1])))).toEvaluateTo(1);
+      expect(toNumber(foldr(sum)(Zero)(fromNumberArray([1])))).toBe(1);
     });
 
     it('folds several items', () => {
       expect(foldr(sum)).toDeferEvaluationOf(Zero, fromNumberArray([1, 2]));
-      expect(toNumber(foldr(sum)(Zero)(fromNumberArray([1, 2])))).toEvaluateTo(3);
+      expect(toNumber(foldr(sum)(Zero)(fromNumberArray([1, 2])))).toBe(3);
     });
 
     it('handles infinite lists', () => {
-      expect(foldr<number, number>(x => a =>
-        iif<number>
+      expect(foldr<Lazy<number>, Lazy<number>>(x => a =>
+        iif<Lazy<number>>
           (x.then(x => fromBoolean(x === 0)))
           (x)
           (x.then(x => a.then(a => _(x + a))))
@@ -144,22 +141,22 @@ describe('List', () => {
   describe('foldrz', () => {
     it('does not fold empty list', () => {
       expect(() => foldrz(sum)(Nil)).not.toThrow();
-      expect(() => $(toNumber(foldrz(sum)(Nil)))).toThrow();
+      expect(() => toNumber(foldrz(sum)(Nil))).toThrow();
     });
 
     it.failing('folds single item', () => {
       expect(foldrz(sum)).toDeferEvaluationOf(fromNumberArray([1]));
-      expect(toNumber(foldrz(sum)(fromNumberArray([1])))).toEvaluateTo(1);
+      expect(toNumber(foldrz(sum)(fromNumberArray([1])))).toBe(1);
     });
 
     it.failing('folds several items', () => {
       expect(foldrz(sum)).toDeferEvaluationOf(fromNumberArray([1, 2]));
-      expect(toNumber(foldrz(sum)(fromNumberArray([1, 2])))).toEvaluateTo(3);
+      expect(toNumber(foldrz(sum)(fromNumberArray([1, 2])))).toBe(3);
     });
 
     it.failing('handles infinite lists', () => {
-      expect(foldrz<number>(x => a =>
-        iif<number>
+      expect(foldrz<Lazy<number>>(x => a =>
+        iif<Lazy<number>>
           (x.then(x => fromBoolean(x === 0)))
           (x)
           (x.then(x => a.then(a => _(x + a))))
@@ -170,42 +167,42 @@ describe('List', () => {
   describe('map', () => {
     it('maps empty list', () => {
       expect(map(succ)).toDeferEvaluationOf(fromNumberArray([]));
-      expect(toNumberArray(map(succ)(fromNumberArray([])))).toEvaluateTo([]);
+      expect(toNumberArray(map(succ)(fromNumberArray([])))).toEqual([]);
     });
 
     it('maps only item', () => {
       expect(map(succ)).toDeferEvaluationOf(fromNumberArray([0]));
-      expect(toNumberArray(map(succ)(fromNumberArray([0])))).toEvaluateTo([1]);
+      expect(toNumberArray(map(succ)(fromNumberArray([0])))).toEqual([1]);
     });
 
     it('maps several items', () => {
       expect(map(succ)).toDeferEvaluationOf(fromNumberArray([0, 1]));
-      expect(toNumberArray(map(succ)(fromNumberArray([0, 1])))).toEvaluateTo([1, 2]);
+      expect(toNumberArray(map(succ)(fromNumberArray([0, 1])))).toEqual([1, 2]);
     });
 
     it('handles infinite lists', () => {
-      expect(toNumber(head(map(succ)(niterate(Zero))))).toEvaluateTo(1);
+      expect(toNumber(head(map(succ)(niterate(Zero))))).toBe(1);
     });
   });
 
   describe('filter', () => {
     it('filter empty list', () => {
       expect(filter(odd)).toDeferEvaluationOf(fromNumberArray([]));
-      expect(toNumberArray(filter(odd)(fromNumberArray([])))).toEvaluateTo([]);
+      expect(toNumberArray(filter(odd)(fromNumberArray([])))).toEqual([]);
     });
 
     it('filters only item', () => {
       expect(filter(odd)).toDeferEvaluationOf(fromNumberArray([0]));
-      expect(toNumberArray(filter(odd)(fromNumberArray([])))).toEvaluateTo([]);
+      expect(toNumberArray(filter(odd)(fromNumberArray([])))).toEqual([]);
     });
 
     it('filters several items', () => {
       expect(filter(odd)).toDeferEvaluationOf(fromNumberArray([0, 1]));
-      expect(toNumberArray(filter(odd)(fromNumberArray([0, 1])))).toEvaluateTo([1]);
+      expect(toNumberArray(filter(odd)(fromNumberArray([0, 1])))).toEqual([1]);
     });
 
     it('handles infinite lists', () => {
-      expect(toNumber(head(filter(odd)(niterate(Zero))))).toEvaluateTo(1);
+      expect(toNumber(head(filter(odd)(niterate(Zero))))).toBe(1);
     });
   });
 });
diff --git a/test/num.spec.ts b/test/num.spec.ts
index 3670630..fbfa0bb 100644
--- a/test/num.spec.ts
+++ b/test/num.spec.ts
@@ -1,36 +1,33 @@
 import { describe, expect, it } from '@jest/globals';
-import { _, Lazy } from '../src/core';
+import { _ } from '../src/core';
 import { Num, Zero, Succ, sum, succ, pred, ifz, fromNumber, toNumber, sub, mul } from '../src/num';
 
 describe('Num', () => {
   describe('toNumber', () => {
     it('converts 0', () => {
-      expect(toNumber).toDeferEvaluationOf(Zero);
-      expect(toNumber(Zero)).toEvaluateTo(0);
+      expect(toNumber(Zero)).toBe(0);
     });
 
     it('converts 1', () => {
-      expect(toNumber).toDeferEvaluationOf(Succ(Zero));
-      expect(toNumber(Succ(Zero))).toEvaluateTo(1);
+      expect(toNumber(Succ(Zero))).toBe(1);
     });
 
     it('converts 2', () => {
-      expect(toNumber).toDeferEvaluationOf(Succ(Succ(Zero)));
-      expect(toNumber(Succ(Succ(Zero)))).toEvaluateTo(2);
+      expect(toNumber(Succ(Succ(Zero)))).toBe(2);
     });
   });
 
   describe('fromNumber', () => {
     it('converts 0', () => {
-      expect(toNumber(fromNumber(0))).toEvaluateTo(0);
+      expect(toNumber(fromNumber(0))).toBe(0);
     });
 
     it('converts 1', () => {
-      expect(toNumber(fromNumber(1))).toEvaluateTo(1);
+      expect(toNumber(fromNumber(1))).toBe(1);
     });
 
     it('converts 2', () => {
-      expect(toNumber(fromNumber(2))).toEvaluateTo(2);
+      expect(toNumber(fromNumber(2))).toBe(2);
     });
   });
 
@@ -51,7 +48,7 @@ describe('Num', () => {
     });
 
     it('deeply lazy', () => {
-      const alot: Lazy<Num> = fromNumber(1000000);
+      const alot: Num = fromNumber(1000000);
       expect(ifz(Succ(alot))(_(true))(_(false))).toEvaluateTo(false);
       expect(alot.evaluated).toBe(false);
     });
@@ -60,110 +57,110 @@ describe('Num', () => {
   describe('succ', () => {
     it('succ 0 is 1', () => {
       expect(succ).toDeferEvaluationOf(fromNumber(0));
-      expect(toNumber(succ(fromNumber(0)))).toEvaluateTo(1);
+      expect(toNumber(succ(fromNumber(0)))).toBe(1);
     });
 
     it('succ 1 is 2', () => {
       expect(succ).toDeferEvaluationOf(fromNumber(0));
-      expect(toNumber(succ(fromNumber(1)))).toEvaluateTo(2);
+      expect(toNumber(succ(fromNumber(1)))).toBe(2);
     });
 
     it('succ 10 is 11', () => {
       expect(succ).toDeferEvaluationOf(fromNumber(10));
-      expect(toNumber(succ(fromNumber(10)))).toEvaluateTo(11);
+      expect(toNumber(succ(fromNumber(10)))).toBe(11);
     });
   });
 
   describe('pred', () => {
     it('pred 0 is 0', () => {
       expect(pred).toDeferEvaluationOf(fromNumber(0));
-      expect(toNumber(pred(fromNumber(0)))).toEvaluateTo(0);
+      expect(toNumber(pred(fromNumber(0)))).toBe(0);
     });
 
     it('pred 1 is 0', () => {
       expect(pred).toDeferEvaluationOf(fromNumber(0));
-      expect(toNumber(pred(fromNumber(1)))).toEvaluateTo(0);
+      expect(toNumber(pred(fromNumber(1)))).toBe(0);
     });
 
     it('pred 10 is 9', () => {
       expect(pred).toDeferEvaluationOf(fromNumber(10));
-      expect(toNumber(pred(fromNumber(10)))).toEvaluateTo(9);
+      expect(toNumber(pred(fromNumber(10)))).toBe(9);
     });
   });
 
   describe('sum', () => {
     it('0 sum 0 is 0', () => {
       expect(sum).toDeferEvaluationOf(fromNumber(0), fromNumber(0));
-      expect(toNumber(sum(fromNumber(0))(fromNumber(0)))).toEvaluateTo(0);
+      expect(toNumber(sum(fromNumber(0))(fromNumber(0)))).toBe(0);
     });
 
     it('0 sum 1 is 1', () => {
       expect(sum).toDeferEvaluationOf(fromNumber(0), fromNumber(1));
-      expect(toNumber(sum(fromNumber(0))(fromNumber(1)))).toEvaluateTo(1);
+      expect(toNumber(sum(fromNumber(0))(fromNumber(1)))).toBe(1);
     });
 
     it('1 sum 0 is 1', () => {
       expect(sum).toDeferEvaluationOf(fromNumber(1), fromNumber(0));
-      expect(toNumber(sum(fromNumber(1))(fromNumber(0)))).toEvaluateTo(1);
+      expect(toNumber(sum(fromNumber(1))(fromNumber(0)))).toBe(1);
     });
 
     it('3 sum 4 is 7', () => {
       expect(sum).toDeferEvaluationOf(fromNumber(3), fromNumber(4));
-      expect(toNumber(sum(fromNumber(3))(fromNumber(4)))).toEvaluateTo(7);
+      expect(toNumber(sum(fromNumber(3))(fromNumber(4)))).toBe(7);
     });
   });
 
   describe('sub', () => {
     it('0 sub 0 is 0', () => {
       expect(sub).toDeferEvaluationOf(fromNumber(0), fromNumber(0));
-      expect(toNumber(sub(fromNumber(0))(fromNumber(0)))).toEvaluateTo(0);
+      expect(toNumber(sub(fromNumber(0))(fromNumber(0)))).toBe(0);
     });
 
     it('0 sub 1 is 0', () => {
       expect(sub).toDeferEvaluationOf(fromNumber(0), fromNumber(1));
-      expect(toNumber(sub(fromNumber(0))(fromNumber(1)))).toEvaluateTo(0);
+      expect(toNumber(sub(fromNumber(0))(fromNumber(1)))).toBe(0);
     });
 
     it('1 sub 0 is 1', () => {
       expect(sub).toDeferEvaluationOf(fromNumber(1), fromNumber(0));
-      expect(toNumber(sub(fromNumber(1))(fromNumber(0)))).toEvaluateTo(1);
+      expect(toNumber(sub(fromNumber(1))(fromNumber(0)))).toBe(1);
     });
 
     it('7 sub 4 is 3', () => {
       expect(sub).toDeferEvaluationOf(fromNumber(7), fromNumber(4));
-      expect(toNumber(sub(fromNumber(7))(fromNumber(4)))).toEvaluateTo(3);
+      expect(toNumber(sub(fromNumber(7))(fromNumber(4)))).toBe(3);
     });
   });
 
   describe('mul', () => {
     it('0 mul 0 is 0', () => {
       expect(mul).toDeferEvaluationOf(fromNumber(0), fromNumber(0));
-      expect(toNumber(mul(fromNumber(0))(fromNumber(0)))).toEvaluateTo(0);
+      expect(toNumber(mul(fromNumber(0))(fromNumber(0)))).toBe(0);
     });
 
     it('0 mul 10 is 0', () => {
       expect(mul).toDeferEvaluationOf(fromNumber(0), expect.skipped(fromNumber(10)));
-      expect(toNumber(mul(fromNumber(0))(fromNumber(10)))).toEvaluateTo(0);
+      expect(toNumber(mul(fromNumber(0))(fromNumber(10)))).toBe(0);
     });
 
     it('10 mul 0 is 0', () => {
       expect(mul).toDeferEvaluationOf(fromNumber(10), fromNumber(0));
-      expect(toNumber(mul(fromNumber(1))(fromNumber(0)))).toEvaluateTo(0);
+      expect(toNumber(mul(fromNumber(1))(fromNumber(0)))).toBe(0);
     });
 
     it('1 mul 10 is 10', () => {
       expect(mul).toDeferEvaluationOf(fromNumber(1), fromNumber(10));
-      expect(toNumber(mul(fromNumber(1))(fromNumber(10)))).toEvaluateTo(10);
+      expect(toNumber(mul(fromNumber(1))(fromNumber(10)))).toBe(10);
     });
 
     it('10 mul 1 is 10', () => {
       expect(mul).toDeferEvaluationOf(fromNumber(10), fromNumber(1));
-      expect(toNumber(mul(fromNumber(10))(fromNumber(1)))).toEvaluateTo(10);
+      expect(toNumber(mul(fromNumber(10))(fromNumber(1)))).toBe(10);
     });
 
     it('3 mul 4 is 12', () => {
       expect(mul).toDeferEvaluationOf(fromNumber(3), fromNumber(4));
-      expect(toNumber(mul(fromNumber(3))(fromNumber(4)))).toEvaluateTo(12);
+      expect(toNumber(mul(fromNumber(3))(fromNumber(4)))).toBe(12);
     });
   });
 });