Added multivariate abstractions.

kmath-functions/src/commonMain/kotlin/space/kscience/kmath/functions/LabeledPolynomial.kt

@@ -117,8 +117,8 @@ public fun <C> C.asLabeledPolynomial() : LabeledPolynomial<C> = LabeledPolynomia
  */
 public class LabeledPolynomialSpace<C, A : Ring<C>>(
     public override val ring: A,
-) : PolynomialSpaceOverRing<C, LabeledPolynomial<C>, A> {
+) : MultivariatePolynomialSpace<C, Symbol, LabeledPolynomial<C>>, PolynomialSpaceOverRing<C, LabeledPolynomial<C>, A> {
-    public operator fun Symbol.plus(other: Int): LabeledPolynomial<C> =
+    public override operator fun Symbol.plus(other: Int): LabeledPolynomial<C> =
         if (other == 0) LabeledPolynomial<C>(mapOf(
             mapOf(this@plus to 1U) to constantOne,
         ))
@@ -126,7 +126,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(this@plus to 1U) to constantOne,
             emptyMap<Symbol, UInt>() to constantOne * other,
         ))
-    public operator fun Symbol.minus(other: Int): LabeledPolynomial<C> =
+    public override operator fun Symbol.minus(other: Int): LabeledPolynomial<C> =
         if (other == 0) LabeledPolynomial<C>(mapOf(
             mapOf(this@minus to 1U) to -constantOne,
         ))
@@ -134,13 +134,13 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(this@minus to 1U) to -constantOne,
             emptyMap<Symbol, UInt>() to constantOne * other,
         ))
-    public operator fun Symbol.times(other: Int): LabeledPolynomial<C> =
+    public override operator fun Symbol.times(other: Int): LabeledPolynomial<C> =
         if (other == 0) zero
         else LabeledPolynomial<C>(mapOf(
             mapOf(this to 1U) to constantOne * other,
         ))
 
-    public operator fun Int.plus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun Int.plus(other: Symbol): LabeledPolynomial<C> =
         if (this == 0) LabeledPolynomial<C>(mapOf(
             mapOf(other to 1U) to constantOne,
         ))
@@ -148,7 +148,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(other to 1U) to constantOne,
             emptyMap<Symbol, UInt>() to constantOne * this@plus,
         ))
-    public operator fun Int.minus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun Int.minus(other: Symbol): LabeledPolynomial<C> =
         if (this == 0) LabeledPolynomial<C>(mapOf(
             mapOf(other to 1U) to -constantOne,
         ))
@@ -156,7 +156,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(other to 1U) to -constantOne,
             emptyMap<Symbol, UInt>() to constantOne * this@minus,
         ))
-    public operator fun Int.times(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun Int.times(other: Symbol): LabeledPolynomial<C> =
         if (this == 0) zero
         else LabeledPolynomial<C>(mapOf(
             mapOf(other to 1U) to constantOne * this@times,
@@ -275,7 +275,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
      */
     public override fun number(value: Int): LabeledPolynomial<C> = number(constantNumber(value))
 
-    public operator fun C.plus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun C.plus(other: Symbol): LabeledPolynomial<C> =
         if (isZero()) LabeledPolynomial<C>(mapOf(
             mapOf(other to 1U) to constantOne,
         ))
@@ -283,7 +283,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(other to 1U) to constantOne,
             emptyMap<Symbol, UInt>() to this@plus,
         ))
-    public operator fun C.minus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun C.minus(other: Symbol): LabeledPolynomial<C> =
         if (isZero()) LabeledPolynomial<C>(mapOf(
             mapOf(other to 1U) to -constantOne,
         ))
@@ -291,13 +291,13 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(other to 1U) to -constantOne,
             emptyMap<Symbol, UInt>() to this@minus,
         ))
-    public operator fun C.times(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun C.times(other: Symbol): LabeledPolynomial<C> =
         if (isZero()) zero
         else LabeledPolynomial<C>(mapOf(
             mapOf(other to 1U) to this@times,
         ))
 
-    public operator fun Symbol.plus(other: C): LabeledPolynomial<C> =
+    public override operator fun Symbol.plus(other: C): LabeledPolynomial<C> =
         if (other.isZero()) LabeledPolynomial<C>(mapOf(
             mapOf(this@plus to 1U) to constantOne,
         ))
@@ -305,7 +305,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(this@plus to 1U) to constantOne,
             emptyMap<Symbol, UInt>() to other,
         ))
-    public operator fun Symbol.minus(other: C): LabeledPolynomial<C> =
+    public override operator fun Symbol.minus(other: C): LabeledPolynomial<C> =
         if (other.isZero()) LabeledPolynomial<C>(mapOf(
             mapOf(this@minus to 1U) to -constantOne,
         ))
@@ -313,7 +313,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(this@minus to 1U) to -constantOne,
             emptyMap<Symbol, UInt>() to other,
         ))
-    public operator fun Symbol.times(other: C): LabeledPolynomial<C> =
+    public override operator fun Symbol.times(other: C): LabeledPolynomial<C> =
         if (other.isZero()) zero
         else LabeledPolynomial<C>(mapOf(
             mapOf(this@times to 1U) to other,
@@ -430,7 +430,15 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
         if (value == 0) zero
         else LabeledPolynomial(mapOf(emptyMap<Symbol, UInt>() to value))
 
-    public operator fun Symbol.plus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun Symbol.unaryPlus(): LabeledPolynomial<C> =
+        LabeledPolynomial<C>(mapOf(
+            mapOf(this to 1U) to constantOne,
+        ))
+    public override operator fun Symbol.unaryMinus(): LabeledPolynomial<C> =
+        LabeledPolynomial<C>(mapOf(
+            mapOf(this to 1U) to -constantOne,
+        ))
+    public override operator fun Symbol.plus(other: Symbol): LabeledPolynomial<C> =
         if (this == other) LabeledPolynomial<C>(mapOf(
             mapOf(this to 1U) to constantOne * 2
         ))
@@ -438,13 +446,13 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(this to 1U) to constantOne,
             mapOf(other to 1U) to constantOne,
         ))
-    public operator fun Symbol.minus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun Symbol.minus(other: Symbol): LabeledPolynomial<C> =
         if (this == other) zero
         else LabeledPolynomial<C>(mapOf(
             mapOf(this to 1U) to constantOne,
             mapOf(other to 1U) to -constantOne,
         ))
-    public operator fun Symbol.times(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun Symbol.times(other: Symbol): LabeledPolynomial<C> =
         if (this == other) LabeledPolynomial<C>(mapOf(
             mapOf(this to 2U) to constantOne
         ))
@@ -452,7 +460,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
             mapOf(this to 1U, other to 1U) to constantOne,
         ))
 
-    public operator fun Symbol.plus(other: LabeledPolynomial<C>): LabeledPolynomial<C> =
+    public override operator fun Symbol.plus(other: LabeledPolynomial<C>): LabeledPolynomial<C> =
         with(other.coefficients) {
             if (isEmpty()) LabeledPolynomial<C>(mapOf(mapOf(this@plus to 1u) to constantOne))
             else LabeledPolynomial<C>(
@@ -467,7 +475,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
                     }
             )
         }
-    public operator fun Symbol.minus(other: LabeledPolynomial<C>): LabeledPolynomial<C> =
+    public override operator fun Symbol.minus(other: LabeledPolynomial<C>): LabeledPolynomial<C> =
         with(other.coefficients) {
             if (isEmpty()) LabeledPolynomial<C>(mapOf(mapOf(this@minus to 1u) to constantOne))
             else LabeledPolynomial<C>(
@@ -484,13 +492,13 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
                     }
             )
         }
-    public operator fun Symbol.times(other: LabeledPolynomial<C>): LabeledPolynomial<C> =
+    public override operator fun Symbol.times(other: LabeledPolynomial<C>): LabeledPolynomial<C> =
         LabeledPolynomial<C>(
             other.coefficients
                 .mapKeys { (degs, _) -> degs.toMutableMap().also{ it[this] = if (this in it) it[this]!! + 1U else 1U } }
         )
 
-    public operator fun LabeledPolynomial<C>.plus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun LabeledPolynomial<C>.plus(other: Symbol): LabeledPolynomial<C> =
         with(coefficients) {
             if (isEmpty()) LabeledPolynomial<C>(mapOf(mapOf(other to 1u) to constantOne))
             else LabeledPolynomial<C>(
@@ -505,7 +513,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
                     }
             )
         }
-    public operator fun LabeledPolynomial<C>.minus(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun LabeledPolynomial<C>.minus(other: Symbol): LabeledPolynomial<C> =
         with(coefficients) {
             if (isEmpty()) LabeledPolynomial<C>(mapOf(mapOf(other to 1u) to constantOne))
             else LabeledPolynomial<C>(
@@ -520,7 +528,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
                     }
             )
         }
-    public operator fun LabeledPolynomial<C>.times(other: Symbol): LabeledPolynomial<C> =
+    public override operator fun LabeledPolynomial<C>.times(other: Symbol): LabeledPolynomial<C> =
         LabeledPolynomial<C>(
             coefficients
                 .mapKeys { (degs, _) -> degs.toMutableMap().also{ it[other] = if (other in it) it[other]!! + 1U else 1U } }
@@ -604,7 +612,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
      * As consequence all values in the map are positive integers. Also, if the polynomial is constant, the map is empty.
      * And keys of the map is the same as in [variables].
      */
-    public val LabeledPolynomial<C>.degrees: Map<Symbol, UInt>
+    public override val LabeledPolynomial<C>.degrees: Map<Symbol, UInt>
         get() =
             buildMap {
                 coefficients.entries.forEach { (degs, c) ->
@@ -613,10 +621,20 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
                     }
                 }
             }
+    /**
+     * Counts degree of the polynomial by the specified [variable].
+     */
+    public override fun LabeledPolynomial<C>.degreeBy(variable: Symbol): UInt =
+        coefficients.entries.maxOfOrNull { (degs, c) -> if (c.isZero()) 0u else degs.getOrElse(variable) { 0u } } ?: 0u
+    /**
+     * Counts degree of the polynomial by the specified [variables].
+     */
+    public override fun LabeledPolynomial<C>.degreeBy(variables: Collection<Symbol>): UInt =
+        coefficients.entries.maxOfOrNull { (degs, c) -> if (c.isZero()) 0u else degs.filterKeys { it in variables }.values.sum() } ?: 0u
     /**
      * Set of all variables that appear in the polynomial in positive exponents.
      */
-    public val LabeledPolynomial<C>.variables: Set<Symbol>
+    public override val LabeledPolynomial<C>.variables: Set<Symbol>
         get() =
             buildSet {
                 coefficients.entries.forEach { (degs, c) -> if (c.isNotZero()) addAll(degs.keys) }
@@ -624,7 +642,7 @@ public class LabeledPolynomialSpace<C, A : Ring<C>>(
     /**
      * Count of all variables that appear in the polynomial in positive exponents.
      */
-    public val LabeledPolynomial<C>.countOfVariables: Int get() = variables.size
+    public override val LabeledPolynomial<C>.countOfVariables: Int get() = variables.size
 
     /**
      * Checks if the instant is constant polynomial (of degree no more than 0) over considered ring.

kmath-functions/src/commonMain/kotlin/space/kscience/kmath/functions/LabeledRationalFunction.kt

@@ -63,14 +63,16 @@ public fun <C, A: Ring<C>> A.LabeledRationalFunction(numeratorCoefficients: Map<
 public class LabeledRationalFunctionSpace<C, A: Ring<C>>(
     public val ring: A,
 ) :
-    RationalFunctionalSpaceOverPolynomialSpace<
+    MultivariateRationalFunctionalSpaceOverMultivariatePolynomialSpace<
             C,
+            Symbol,
             LabeledPolynomial<C>,
             LabeledRationalFunction<C>,
             LabeledPolynomialSpace<C, A>,
             >,
-    PolynomialSpaceOfFractions<
+    MultivariatePolynomialSpaceOfFractions<
             C,
+            Symbol,
             LabeledPolynomial<C>,
             LabeledRationalFunction<C>,
             >() {
@@ -113,33 +115,6 @@ public class LabeledRationalFunctionSpace<C, A: Ring<C>>(
         return numerator * other.denominator equalsTo other.numerator * denominator
     }
 
-    /**
-     * Map that associates variables (that appear in the polynomial in positive exponents) with their most exponents
-     * in which they are appeared in the polynomial.
-     *
-     * As consequence all values in the map are positive integers. Also, if the polynomial is constant, the map is empty.
-     * And keys of the map is the same as in [variables].
-     */
-    public val LabeledPolynomial<C>.degrees: Map<Symbol, UInt> get() = polynomialRing { degrees }
-    /**
-     * Set of all variables that appear in the polynomial in positive exponents.
-     */
-    public val LabeledPolynomial<C>.variables: Set<Symbol> get() = polynomialRing { variables }
-    /**
-     * Count of all variables that appear in the polynomial in positive exponents.
-     */
-    public val LabeledPolynomial<C>.countOfVariables: Int get() = polynomialRing { countOfVariables }
-
-    /**
-     * Count of all variables that appear in the polynomial in positive exponents.
-     */
-    public val LabeledRationalFunction<C>.variables: Set<Symbol>
-        get() = numerator.variables union denominator.variables
-    /**
-     * Count of all variables that appear in the polynomial in positive exponents.
-     */
-    public val LabeledRationalFunction<C>.countOfVariables: Int get() = variables.size
-
     // TODO: Разобрать
 
 //    operator fun invoke(arg: Map<Symbol, C>): LabeledRationalFunction<C> =

kmath-functions/src/commonMain/kotlin/space/kscience/kmath/functions/Polynomial.kt

@@ -5,7 +5,8 @@
 
 package space.kscience.kmath.functions
 
-import space.kscience.kmath.operations.*
+import space.kscience.kmath.operations.Ring
+import space.kscience.kmath.operations.invoke
 import kotlin.js.JsName
 import kotlin.jvm.JvmName
 
@@ -414,3 +415,60 @@ public interface PolynomialSpaceOverRing<C, P: Polynomial<C>, A: Ring<C>> : Poly
      */
     public override val constantOne: C get() = ring.one
 }
+
+public interface MultivariatePolynomialSpace<C, V, P: Polynomial<C>>: PolynomialSpace<C, P> {
+    public operator fun V.plus(other: Int): P
+    public operator fun V.minus(other: Int): P
+    public operator fun V.times(other: Int): P
+
+    public operator fun Int.plus(other: V): P
+    public operator fun Int.minus(other: V): P
+    public operator fun Int.times(other: V): P
+
+    public operator fun C.plus(other: V): P
+    public operator fun C.minus(other: V): P
+    public operator fun C.times(other: V): P
+
+    public operator fun V.plus(other: C): P
+    public operator fun V.minus(other: C): P
+    public operator fun V.times(other: C): P
+
+    public operator fun V.unaryPlus(): P
+    public operator fun V.unaryMinus(): P
+    public operator fun V.plus(other: V): P
+    public operator fun V.minus(other: V): P
+    public operator fun V.times(other: V): P
+
+    public operator fun V.plus(other: P): P
+    public operator fun V.minus(other: P): P
+    public operator fun V.times(other: P): P
+
+    public operator fun P.plus(other: V): P
+    public operator fun P.minus(other: V): P
+    public operator fun P.times(other: V): P
+
+    /**
+     * Map that associates variables (that appear in the polynomial in positive exponents) with their most exponents
+     * in which they are appeared in the polynomial.
+     *
+     * As consequence all values in the map are positive integers. Also, if the polynomial is constant, the map is empty.
+     * And keys of the map is the same as in [variables].
+     */
+    public val P.degrees: Map<V, UInt>
+    /**
+     * Counts degree of the polynomial by the specified [variable].
+     */
+    public fun P.degreeBy(variable: V): UInt = degrees.getOrElse(variable) { 0u }
+    /**
+     * Counts degree of the polynomial by the specified [variables].
+     */
+    public fun P.degreeBy(variables: Collection<V>): UInt
+    /**
+     * Set of all variables that appear in the polynomial in positive exponents.
+     */
+    public val P.variables: Set<V> get() = degrees.keys
+    /**
+     * Count of all variables that appear in the polynomial in positive exponents.
+     */
+    public val P.countOfVariables: Int get() = variables.size
+}

kmath-functions/src/commonMain/kotlin/space/kscience/kmath/functions/RationalFunction.kt

@@ -1307,3 +1307,200 @@ public abstract class PolynomialSpaceOfFractions<
      */
     public override val one: R get() = constructRationalFunction(polynomialOne)
 }
+
+public interface MultivariateRationalFunctionalSpace<
+        C,
+        V,
+        P: Polynomial<C>,
+        R: RationalFunction<C, P>
+        >: RationalFunctionalSpace<C, P, R> {
+    public operator fun V.plus(other: Int): P
+    public operator fun V.minus(other: Int): P
+    public operator fun V.times(other: Int): P
+
+    public operator fun Int.plus(other: V): P
+    public operator fun Int.minus(other: V): P
+    public operator fun Int.times(other: V): P
+
+    public operator fun C.plus(other: V): P
+    public operator fun C.minus(other: V): P
+    public operator fun C.times(other: V): P
+
+    public operator fun V.plus(other: C): P
+    public operator fun V.minus(other: C): P
+    public operator fun V.times(other: C): P
+
+    public operator fun V.unaryPlus(): P
+    public operator fun V.unaryMinus(): P
+    public operator fun V.plus(other: V): P
+    public operator fun V.minus(other: V): P
+    public operator fun V.times(other: V): P
+
+    public operator fun V.plus(other: P): P
+    public operator fun V.minus(other: P): P
+    public operator fun V.times(other: P): P
+
+    public operator fun P.plus(other: V): P
+    public operator fun P.minus(other: V): P
+    public operator fun P.times(other: V): P
+
+    public operator fun V.plus(other: R): R
+    public operator fun V.minus(other: R): R
+    public operator fun V.times(other: R): R
+
+    public operator fun R.plus(other: V): R
+    public operator fun R.minus(other: V): R
+    public operator fun R.times(other: V): R
+
+    /**
+     * Map that associates variables (that appear in the polynomial in positive exponents) with their most exponents
+     * in which they are appeared in the polynomial.
+     *
+     * As consequence all values in the map are positive integers. Also, if the polynomial is constant, the map is empty.
+     * And keys of the map is the same as in [variables].
+     */
+    public val P.degrees: Map<V, UInt>
+    /**
+     * Counts degree of the polynomial by the specified [variable].
+     */
+    public fun P.degreeBy(variable: V): UInt = degrees.getOrElse(variable) { 0u }
+    /**
+     * Counts degree of the polynomial by the specified [variables].
+     */
+    public fun P.degreeBy(variables: Collection<V>): UInt
+    /**
+     * Set of all variables that appear in the polynomial in positive exponents.
+     */
+    public val P.variables: Set<V> get() = degrees.keys
+    /**
+     * Count of all variables that appear in the polynomial in positive exponents.
+     */
+    public val P.countOfVariables: Int get() = variables.size
+
+    /**
+     * Set of all variables that appear in the polynomial in positive exponents.
+     */
+    public val R.variables: Set<V> get() = numerator.variables union denominator.variables
+    /**
+     * Count of all variables that appear in the polynomial in positive exponents.
+     */
+    public val R.countOfVariables: Int get() = variables.size
+}
+
+public interface MultivariateRationalFunctionalSpaceOverRing<
+        C,
+        V,
+        P: Polynomial<C>,
+        R: RationalFunction<C, P>,
+        A: Ring<C>
+        > : RationalFunctionalSpaceOverRing<C, P, R, A>, MultivariateRationalFunctionalSpace<C, V, P, R>
+
+public interface MultivariateRationalFunctionalSpaceOverPolynomialSpace<
+        C,
+        V,
+        P: Polynomial<C>,
+        R: RationalFunction<C, P>,
+        AP: PolynomialSpace<C, P>,
+        > : RationalFunctionalSpaceOverPolynomialSpace<C, P, R, AP>, MultivariateRationalFunctionalSpace<C, V, P, R>
+
+public interface MultivariateRationalFunctionalSpaceOverMultivariatePolynomialSpace<
+        C,
+        V,
+        P: Polynomial<C>,
+        R: RationalFunction<C, P>,
+        AP: MultivariatePolynomialSpace<C, V, P>,
+        > : MultivariateRationalFunctionalSpaceOverPolynomialSpace<C, V, P, R, AP> {
+    public override operator fun V.plus(other: Int): P = polynomialRing { this@plus + other }
+    public override operator fun V.minus(other: Int): P = polynomialRing { this@minus - other }
+    public override operator fun V.times(other: Int): P = polynomialRing { this@times * other }
+
+    public override operator fun Int.plus(other: V): P = polynomialRing { this@plus + other }
+    public override operator fun Int.minus(other: V): P = polynomialRing { this@minus - other }
+    public override operator fun Int.times(other: V): P = polynomialRing { this@times * other }
+
+    public override operator fun C.plus(other: V): P = polynomialRing { this@plus + other }
+    public override operator fun C.minus(other: V): P = polynomialRing { this@minus - other }
+    public override operator fun C.times(other: V): P = polynomialRing { this@times * other }
+
+    public override operator fun V.plus(other: C): P = polynomialRing { this@plus + other }
+    public override operator fun V.minus(other: C): P = polynomialRing { this@minus - other }
+    public override operator fun V.times(other: C): P = polynomialRing { this@times * other }
+
+    public override operator fun V.unaryPlus(): P = polynomialRing { +this@unaryPlus }
+    public override operator fun V.unaryMinus(): P = polynomialRing { -this@unaryMinus }
+    public override operator fun V.plus(other: V): P = polynomialRing { this@plus + other }
+    public override operator fun V.minus(other: V): P = polynomialRing { this@minus - other }
+    public override operator fun V.times(other: V): P = polynomialRing { this@times * other }
+
+    public override operator fun V.plus(other: P): P = polynomialRing { this@plus + other }
+    public override operator fun V.minus(other: P): P = polynomialRing { this@minus - other }
+    public override operator fun V.times(other: P): P = polynomialRing { this@times * other }
+
+    public override operator fun P.plus(other: V): P = polynomialRing { this@plus + other }
+    public override operator fun P.minus(other: V): P = polynomialRing { this@minus - other }
+    public override operator fun P.times(other: V): P = polynomialRing { this@times * other }
+
+    /**
+     * Map that associates variables (that appear in the polynomial in positive exponents) with their most exponents
+     * in which they are appeared in the polynomial.
+     *
+     * As consequence all values in the map are positive integers. Also, if the polynomial is constant, the map is empty.
+     * And keys of the map is the same as in [variables].
+     */
+    public override val P.degrees: Map<V, UInt> get() = polynomialRing { degrees }
+    /**
+     * Counts degree of the polynomial by the specified [variable].
+     */
+    public override fun P.degreeBy(variable: V): UInt = polynomialRing { degreeBy(variable) }
+    /**
+     * Counts degree of the polynomial by the specified [variables].
+     */
+    public override fun P.degreeBy(variables: Collection<V>): UInt = polynomialRing { degreeBy(variables) }
+    /**
+     * Set of all variables that appear in the polynomial in positive exponents.
+     */
+    public override val P.variables: Set<V> get() = polynomialRing { variables }
+    /**
+     * Count of all variables that appear in the polynomial in positive exponents.
+     */
+    public override val P.countOfVariables: Int get() = polynomialRing { countOfVariables }
+}
+
+public abstract class MultivariatePolynomialSpaceOfFractions<
+        C,
+        V,
+        P: Polynomial<C>,
+        R: RationalFunction<C, P>,
+        > : MultivariateRationalFunctionalSpace<C, V, P, R>,  PolynomialSpaceOfFractions<C, P, R>() {
+    public override operator fun V.plus(other: R): R =
+        constructRationalFunction(
+            this * other.denominator + other.numerator,
+            other.denominator
+        )
+    public override operator fun V.minus(other: R): R =
+        constructRationalFunction(
+            this * other.denominator - other.numerator,
+            other.denominator
+        )
+    public override operator fun V.times(other: R): R =
+        constructRationalFunction(
+            this * other.numerator,
+            other.denominator
+        )
+
+    public override operator fun R.plus(other: V): R =
+        constructRationalFunction(
+            numerator + denominator * other,
+            denominator
+        )
+    public override operator fun R.minus(other: V): R =
+        constructRationalFunction(
+            numerator - denominator * other,
+            denominator
+        )
+    public override operator fun R.times(other: V): R =
+        constructRationalFunction(
+            numerator * other,
+            denominator
+        )
+}