+ When we add two EJA operators, we get another one back::
+
+ sage: J = RealSymmetricEJA(2)
+ sage: id = identity_matrix(J.base_ring(), J.dimension())
+ sage: f = FiniteDimensionalEuclideanJordanAlgebraOperator(J,J,id)
+ sage: g = FiniteDimensionalEuclideanJordanAlgebraOperator(J,J,id)
+ sage: f + g
+ Linear operator between finite-dimensional Euclidean Jordan
+ algebras represented by the matrix:
+ [2 0 0]
+ [0 2 0]
+ [0 0 2]
+ Domain: Euclidean Jordan algebra of degree 3 over Rational Field
+ Codomain: Euclidean Jordan algebra of degree 3 over Rational Field
+
+ If you try to add two identical vector space operators but on
+ different EJAs, that should blow up::
+
+ sage: J1 = RealSymmetricEJA(2)
+ sage: J2 = JordanSpinEJA(3)
+ sage: id = identity_matrix(QQ, 3)
+ sage: f = FiniteDimensionalEuclideanJordanAlgebraOperator(J1,J1,id)
+ sage: g = FiniteDimensionalEuclideanJordanAlgebraOperator(J2,J2,id)
+ sage: f + g
+ Traceback (most recent call last):
+ ...
+ ValueError: operator (co)domains must match
+
+ """
+ if not (self._domain_eja == other._domain_eja and
+ self._codomain_eja == other._codomain_eja):
+ raise ValueError("operator (co)domains must match")
+ return FiniteDimensionalEuclideanJordanAlgebraOperator(
+ self._domain_eja,
+ self._codomain_eja,
+ VectorSpaceMorphism.__add__(self,other))
+