*Steradian* | *documentation* SI SolidAngleMeasure. Symbol: sr. It is the *solid* angle of a sphere subtended by a portion of the surface whose area is *equal* to the square of the sphere's radius. Another definition is: the *solid* angle which, having its vertex in the center of the sphere, cuts off an area of the surface of the sphere *equal* to that of a square with sides of length *equal* to the radius of the sphere. *Steradian* = m^2/m^2 = 1 | |

**is an ***instance* of SolidAngleMeasure | |

**is an ***instance* of SystemeInternationalUnit | |

ConstantQuantity | **has axiom** (=> (*instance* ?FUNCTION UnaryConstantFunctionQuantity) (*and* (*domain* ?FUNCTION 1 ConstantQuantity) (*range* ?FUNCTION ConstantQuantity)))
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**is first ***domain* of *MagnitudeFn* | |

**is second ***domain* of *measure* | |

UnitOfMeasure | **has axiom** (=> (*and* (*equal* (*MeasureFn* ?NUMBER ?UNIT) ?QUANT) (*subclass* ?UNIT ?QUANTTYPE) (*not* (*equal* ?QUANTTYPE UnitOfMeasure))) (*subclass* ?QUANT ?QUANTTYPE))
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**has axiom** (=> (*and* (*instance* ?FUNCTION RelationExtendedToQuantities) (*instance* ?FUNCTION BinaryFunction) (*instance* ?NUMBER1 RealNumber) (*instance* ?NUMBER2 RealNumber) (*equal* (*AssignmentFn* ?FUNCTION ?NUMBER1 ?NUMBER2) ?VALUE)) (forall (?UNIT) (=> (*instance* ?UNIT UnitOfMeasure) (*equal* (*AssignmentFn* ?FUNCTION (*MeasureFn* ?NUMBER1 ?UNIT) (*MeasureFn* ?NUMBER2 ?UNIT)) (*MeasureFn* ?VALUE ?UNIT)))))
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**has axiom** (=> (*and* (*instance* ?REL RelationExtendedToQuantities) (*instance* ?REL BinaryRelation) (*instance* ?NUMBER1 RealNumber) (*instance* ?NUMBER2 RealNumber) (*holds* ?REL ?NUMBER1 ?NUMBER2)) (forall (?UNIT) (=> (*instance* ?UNIT UnitOfMeasure) (*holds* ?REL (*MeasureFn* ?NUMBER1 ?UNIT) (*MeasureFn* ?NUMBER2 ?UNIT)))))
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**is second ***domain* of *MeasureFn* | |

PhysicalQuantity | **is partitioned into** ConstantQuantity, FunctionQuantity | |

Abstract | **is ***disjoint* from Physical | |