Description:

• The operator != evaluates to true iff its operands expr1 and expr2 are syntactically unequal and both different from error, constant expressions that are not constants and that evaluate to two different floating-point number with the global precision prec or polynomials that are unequal while automatic expression simplification is activated. The user should be aware of the fact that because of floating-point evaluation, the operator != is not exactly the same as the negation of the mathematical equality. Further, expressions that are polynomials may not be structurally equal when != evaluates to false; in order to obtain purely structural tests, the user should deactivate automatic simplification using autosimplify.
  
  Following the IEEE 754 standard, NaN compares unequal to itself, even though this corresponds to a case when expr1 and expr2 are syntactically equal and different from error. Accordingly, the interval [NaN, NaN] compares unequal to itself.
  
  Note that the expressions !(expr1 != expr2) and expr1 == expr2 do not always evaluate to the same boolean value. See error for details.
• Notice that @NaN@, [@NaN, @NaN@] and error have special properties with respect to comparison for equality with == and !=. See documentation for == for a detailed description.