+ Return the associative subalgebra of the parent EJA generated
+ by this element.
+
+ TESTS::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,10).abs()
+ sage: J = eja_rn(n)
+ sage: x = J.random_element()
+ sage: x.subalgebra_generated_by().is_associative()
+ True
+ sage: J = eja_ln(n)
+ sage: x = J.random_element()
+ sage: x.subalgebra_generated_by().is_associative()
+ True
+