diff --git a/main/src/io/github/iltotore/iron/compileTime.scala b/main/src/io/github/iltotore/iron/compileTime.scala
index 9bdad499..cfdbea77 100644
--- a/main/src/io/github/iltotore/iron/compileTime.scala
+++ b/main/src/io/github/iltotore/iron/compileTime.scala
@@ -10,6 +10,8 @@ import scala.quoted.*
  */
 object compileTime:
 
+  type NumConstant = Int | Long | Float | Double
+
   /**
    * The zero number of the given type.
    * @tparam A the numerical primitive type.
@@ -144,13 +146,32 @@ object compileTime:
    */
   type %[A, B] = NumOp[A, B, int.%, long.%, float.%, double.%]
 
+  /**
+   * Polymorphic `ToDouble`.
+   *
+   * @tparam A the constant type to cast.
+   */
+  type ToDouble[A <: NumConstant] <: Double = A match
+    case Int => int.ToDouble[A]
+    case Long => long.ToDouble[A]
+    case Float => float.ToDouble[A]
+    case Double => A & Double
+
+  /**
+   * Get the `Double` value of the given type.
+   *
+   * @tparam A the type to convert to `Double`.
+   * @return the String representation of the given type. Equivalent to `constValue[ToDouble[A]]`.
+   */
+  transparent inline def doubleValue[A <: NumConstant]: Double = constValue[ToDouble[A]]
+
   /**
    * Get the `String` value of the given type.
    *
    * @tparam A the type to convert to `String`.
    * @return the String representation of the given type. Equivalent to `constValue[ToString[A]]`.
    */
-  inline def stringValue[A]: String = constValue[ToString[A]]
+  transparent inline def stringValue[A]: String = constValue[ToString[A]]
 
   def applyConstraint[A, C, Impl <: Constraint[A, C]](expr: Expr[A], constraintExpr: Expr[Impl])(using Quotes): Expr[Boolean] = // Using quotes directly causes a "deferred inline error"
 
diff --git a/main/src/io/github/iltotore/iron/constraint/numeric.scala b/main/src/io/github/iltotore/iron/constraint/numeric.scala
index 60234244..5ea0325c 100644
--- a/main/src/io/github/iltotore/iron/constraint/numeric.scala
+++ b/main/src/io/github/iltotore/iron/constraint/numeric.scala
@@ -2,10 +2,7 @@ package io.github.iltotore.iron.constraint
 
 import io.github.iltotore.iron.constraint.any.*
 import io.github.iltotore.iron.compileTime.*
-import io.github.iltotore.iron.{==>, Constraint, Implication, IntNumber, Number}
-
-import scala.compiletime.constValue
-import scala.compiletime.ops.any.ToString
+import io.github.iltotore.iron.{==>, Constraint, Implication}
 
 /**
  * Number-related constraints.
@@ -40,6 +37,50 @@ object numeric:
    */
   type LessEqual[V] = (Less[V] | StrictEqual[V]) DescribedAs ("Should be less than or equal to " + V)
 
+  /**
+   * Tests if the input is strictly positive.
+   */
+  type Positive = Greater[0] DescribedAs "Should be strictly positive"
+
+  /**
+   * Tests if the input is strictly negative.
+   */
+  type Negative = Less[0] DescribedAs "Should be strictly negative"
+
+  object Interval:
+
+    /**
+     * Tests if the input is included in `(V1, V2)`
+     * 
+     * @tparam V1 the lower bound, exclusive.
+     * @tparam V2 the upper bound, exclusive.
+     */
+    type Open[V1, V2] = (Greater[V1] & Less[V2]) DescribedAs ("Should be included in (" + V1 + ", " + V2 + ")")
+
+    /**
+     * Tests if the input is included in `(V1, V2]`
+     *
+     * @tparam V1 the lower bound, exclusive.
+     * @tparam V2 the upper bound, inclusive.
+     */
+    type OpenClosed[V1, V2] = (Greater[V1] & LessEqual[V2]) DescribedAs ("Should be included in (" + V1 + ", " + V2 + "]")
+
+    /**
+     * Tests if the input is included in `[V1, V2)`
+     *
+     * @tparam V1 the lower bound, inclusive.
+     * @tparam V2 the upper bound, exclusive.
+     */
+    type ClosedOpen[V1, V2] = (GreaterEqual[V1] & Less[V2]) DescribedAs ("Should be included in [" + V1 + ", " + V2 + ")")
+
+    /**
+     * Tests if the input is included in `[V1, V2]`
+     *
+     * @tparam V1 the lower bound, inclusive.
+     * @tparam V2 the upper bound, inclusive.
+     */
+    type Closed[V1, V2] = (GreaterEqual[V1] & LessEqual[V2]) DescribedAs ("Should be included in [" + V1 + ", " + V2 + "]")
+
   /**
    * Tests if the input is a multiple of V.
    *
@@ -56,21 +97,41 @@ object numeric:
    */
   final class Divide[V]
 
+  /**
+   * Tests if the input is even (a multiple of 2).
+   */
+  type Even = Multiple[2]
+
+  /**
+   * Tests if the input is odd (not a multiple of 2).
+   */
+  type Odd = Not[Even]
+
+  /**
+   * Tests if the input is not a representable number.
+   */
+  final class NaN
+
+  /**
+   * Tests if the input is whether `+infinity` or `-infinity`.
+   */
+  final class Infinity
+
   object Greater:
-    private trait GreaterConstraint[A, V <: A] extends Constraint[A, Greater[V]]:
+    private trait GreaterConstraint[A, V <: NumConstant] extends Constraint[A, Greater[V]]:
       override inline def message: String = "Should be greater than " + stringValue[V]
 
-    inline given [V <: Int]: GreaterConstraint[Int, V] with
-      override inline def test(value: Int): Boolean = value > constValue[V]
+    inline given [V <: NumConstant]: GreaterConstraint[Int, V] with
+      override inline def test(value: Int): Boolean = value > doubleValue[V]
 
-    inline given [V <: Long]: GreaterConstraint[Long, V] with
-      override inline def test(value: Long): Boolean = value > constValue[V]
+    inline given [V <: NumConstant]: GreaterConstraint[Long, V] with
+      override inline def test(value: Long): Boolean = value > doubleValue[V]
 
-    inline given [V <: Float]: GreaterConstraint[Float, V] with
-      override inline def test(value: Float): Boolean = value > constValue[V]
+    inline given [V <: NumConstant]: GreaterConstraint[Float, V] with
+      override inline def test(value: Float): Boolean = value > doubleValue[V]
 
-    inline given [V <: Double]: GreaterConstraint[Double, V] with
-      override inline def test(value: Double): Boolean = value > constValue[V]
+    inline given [V <: NumConstant]: GreaterConstraint[Double, V] with
+      override inline def test(value: Double): Boolean = value > doubleValue[V]
 
     given [V1, V2](using V1 > V2 =:= true): (Greater[V1] ==> Greater[V2]) = Implication()
 
@@ -83,20 +144,20 @@ object numeric:
     given [V1, V2](using V1 >= V2 =:= true): (StrictEqual[V2] ==> Not[Greater[V1]]) = Implication()
 
   object Less:
-    private trait LessConstraint[A, V] extends Constraint[A, Less[V]]:
+    private trait LessConstraint[A, V <: NumConstant] extends Constraint[A, Less[V]]:
       override inline def message: String = "Should be less than " + stringValue[V]
 
-    inline given [V <: Int]: LessConstraint[Int, V] with
-      override inline def test(value: Int): Boolean = value < constValue[V]
+    inline given [V <: NumConstant]: LessConstraint[Int, V] with
+      override inline def test(value: Int): Boolean = value < doubleValue[V]
 
-    inline given [V <: Long]: LessConstraint[Long, V] with
-      override inline def test(value: Long): Boolean = value < constValue[V]
+    inline given [V <: NumConstant]: LessConstraint[Long, V] with
+      override inline def test(value: Long): Boolean = value < doubleValue[V]
 
-    inline given [V <: Float]: LessConstraint[Float, V] with
-      override inline def test(value: Float): Boolean = value < constValue[V]
+    inline given [V <: NumConstant]: LessConstraint[Float, V] with
+      override inline def test(value: Float): Boolean = value < doubleValue[V]
 
-    inline given [V <: Double]: LessConstraint[Double, V] with
-      override inline def test(value: Double): Boolean = value < constValue[V]
+    inline given [V <: NumConstant]: LessConstraint[Double, V] with
+      override inline def test(value: Double): Boolean = value < doubleValue[V]
 
     given [V1, V2](using V1 < V2 =:= true): (Less[V1] ==> Less[V2]) = Implication()
 
@@ -109,35 +170,55 @@ object numeric:
     given [V1, V2](using V1 <= V2 =:= true): (StrictEqual[V2] ==> Not[Less[V1]]) = Implication()
 
   object Multiple:
-    private trait MultipleConstraint[A, V] extends Constraint[A, Multiple[V]]:
+    private trait MultipleConstraint[A, V <: NumConstant] extends Constraint[A, Multiple[V]]:
       override inline def message: String = "Should be a multiple of " + stringValue[V]
 
-    inline given [V <: Int]: MultipleConstraint[Int, V] with
-      override inline def test(value: Int): Boolean = value % constValue[V] == 0
+    inline given [V <: NumConstant]: MultipleConstraint[Int, V] with
+      override inline def test(value: Int): Boolean = value % doubleValue[V] == 0
 
-    inline given [V <: Long]: MultipleConstraint[Long, V] with
-      override inline def test(value: Long): Boolean = value % constValue[V] == 0
+    inline given [V <: NumConstant]: MultipleConstraint[Long, V] with
+      override inline def test(value: Long): Boolean = value % doubleValue[V] == 0
 
-    inline given [V <: Float]: MultipleConstraint[Float, V] with
-      override inline def test(value: Float): Boolean = value % constValue[V] == 0
+    inline given [V <: NumConstant]: MultipleConstraint[Float, V] with
+      override inline def test(value: Float): Boolean = value % doubleValue[V] == 0
 
-    inline given [V <: Double]: MultipleConstraint[Double, V] with
-      override inline def test(value: Double): Boolean = value % constValue[V] == 0
+    inline given [V <: NumConstant]: MultipleConstraint[Double, V] with
+      override inline def test(value: Double): Boolean = value % doubleValue[V] == 0
 
     given [A, V1 <: A, V2 <: A](using V1 % V2 =:= Zero[A]): (Multiple[V1] ==> Multiple[V2]) = Implication()
 
   object Divide:
-    private trait DivideConstraint[A, V] extends Constraint[A, Divide[V]]:
+    private trait DivideConstraint[A, V <: NumConstant] extends Constraint[A, Divide[V]]:
       override inline def message: String = "Should divide " + stringValue[V]
 
-    inline given [V <: Int]: DivideConstraint[Int, V] with
-      override inline def test(value: Int): Boolean = constValue[V] % value == 0
+    inline given [V <: NumConstant]: DivideConstraint[Int, V] with
+      override inline def test(value: Int): Boolean = doubleValue[V] % value == 0
+
+    inline given [V <: NumConstant]: DivideConstraint[Long, V] with
+      override inline def test(value: Long): Boolean = doubleValue[V] % value == 0
+
+    inline given [V <: NumConstant]: DivideConstraint[Float, V] with
+      override inline def test(value: Float): Boolean = doubleValue[V] % value == 0
+
+    inline given [V <: NumConstant]: DivideConstraint[Double, V] with
+      override inline def test(value: Double): Boolean = doubleValue[V] % value == 0
+
+  object NaN:
+    private trait NaNConstraint[A] extends Constraint[A, NaN]:
+      override inline def message: String = "Should be an unrepresentable number"
+
+    inline given NaNConstraint[Float] with
+      override inline def test(value: Float): Boolean = value.isNaN
+
+    inline given NaNConstraint[Double] with
+      override inline def test(value: Double): Boolean = value.isNaN
 
-    inline given [V <: Long]: DivideConstraint[Long, V] with
-      override inline def test(value: Long): Boolean = constValue[V] % value == 0
+  object Infinity:
+    private trait InfinityConstraint[A] extends Constraint[A, Infinity]:
+      override inline def message: String = "Should be -infinity or +infinity"
 
-    inline given [V <: Float]: DivideConstraint[Float, V] with
-      override inline def test(value: Float): Boolean = constValue[V] % value == 0
+    inline given InfinityConstraint[Float] with
+      override inline def test(value: Float): Boolean = value.isInfinity
 
-    inline given [V <: Double]: DivideConstraint[Double, V] with
-      override inline def test(value: Double): Boolean = constValue[V] % value == 0
+    inline given InfinityConstraint[Double] with
+      override inline def test(value: Double): Boolean = value.isInfinity
diff --git a/main/src/io/github/iltotore/iron/package.scala b/main/src/io/github/iltotore/iron/package.scala
index d6db7007..e6c87150 100644
--- a/main/src/io/github/iltotore/iron/package.scala
+++ b/main/src/io/github/iltotore/iron/package.scala
@@ -15,17 +15,6 @@ import scala.util.NotGiven
 
 export io.github.iltotore.iron.constraint.any.*
 
-/**
- * Union of all numerical primitives.
- * This abstraction facilitates the creation of numerical constraints.
- */
-type Number = Byte | Short | Int | Long | Float | Double
-
-/**
- * Union of all integer primitives. This abstraction facilitates the creation of numerical constraints.
- */
-type IntNumber = Byte | Short | Int | Long
-
 /**
  * An Iron type (refined).
  *
diff --git a/main/test/src/io/github/iltotore/iron/testing/NumericSuite.scala b/main/test/src/io/github/iltotore/iron/testing/NumericSuite.scala
index 7d4b1baf..53db6c5b 100644
--- a/main/test/src/io/github/iltotore/iron/testing/NumericSuite.scala
+++ b/main/test/src/io/github/iltotore/iron/testing/NumericSuite.scala
@@ -30,6 +30,40 @@ object NumericSuite extends TestSuite:
       test - -1.assertRefine[LessEqual[0]]
     }
 
+    test("interval") {
+      test("open") {
+        test - 1.assertRefine[Interval.Open[0, 2]]
+        test - 0.assertNotRefine[Interval.Open[0, 2]]
+        test - 2.assertNotRefine[Interval.Open[0, 2]]
+        test - -1.assertNotRefine[Interval.Open[0, 2]]
+        test - 3.assertNotRefine[Interval.Open[0, 2]]
+      }
+
+      test("openClosed") {
+        test - 1.assertRefine[Interval.OpenClosed[0, 2]]
+        test - 2.assertRefine[Interval.OpenClosed[0, 2]]
+        test - 0.assertNotRefine[Interval.OpenClosed[0, 2]]
+        test - -1.assertNotRefine[Interval.OpenClosed[0, 2]]
+        test - 3.assertNotRefine[Interval.OpenClosed[0, 2]]
+      }
+
+      test("closedOpen") {
+        test - 1.assertRefine[Interval.ClosedOpen[0, 2]]
+        test - 0.assertRefine[Interval.ClosedOpen[0, 2]]
+        test - 2.assertNotRefine[Interval.ClosedOpen[0, 2]]
+        test - -1.assertNotRefine[Interval.ClosedOpen[0, 2]]
+        test - 3.assertNotRefine[Interval.ClosedOpen[0, 2]]
+      }
+
+      test("closed") {
+        test - 1.assertRefine[Interval.Closed[0, 2]]
+        test - 2.assertRefine[Interval.Closed[0, 2]]
+        test - 0.assertRefine[Interval.Closed[0, 2]]
+        test - -1.assertNotRefine[Interval.Closed[0, 2]]
+        test - 3.assertNotRefine[Interval.Closed[0, 2]]
+      }
+    }
+
     test("multiple") {
       test - 1.assertNotRefine[Multiple[2]]
       test - 2.assertRefine[Multiple[2]]
@@ -40,4 +74,20 @@ object NumericSuite extends TestSuite:
       test - 2.assertRefine[Divide[2]]
       test - 3.assertNotRefine[Divide[2]]
     }
+
+    test("nan") {
+      test - Float.NaN.assertRefine[NaN]
+      test - Double.NaN.assertRefine[NaN]
+      test - 0f.assertNotRefine[NaN]
+      test - 0d.assertNotRefine[NaN]
+    }
+
+    test("infinity") {
+      test - Float.PositiveInfinity.assertRefine[Infinity]
+      test - Float.NegativeInfinity.assertRefine[Infinity]
+      test - Double.PositiveInfinity.assertRefine[Infinity]
+      test - Double.NegativeInfinity.assertRefine[Infinity]
+      test - 0f.assertNotRefine[Infinity]
+      test - 0d.assertNotRefine[Infinity]
+    }
   }