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"When all else fails, RTFM..."

sage: x.is_infinity?
Docstring:     
   Return "True" if "self" is an infinite expression.

   EXAMPLES:

      sage: SR(oo).is_infinity()
      True
      sage: x.is_infinity()
      False
Init docstring: Initialize self.  See help(type(self)) for accurate signature.
File:           /usr/local/sage-10/src/sage/symbolic/expression.pyx
Type:           builtin_function_or_method

Illustration :

sage: foo=(1/x).limit(x=0)
sage: foo.is_infinity()
True

Note that :

sage: bool(foo>0)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[7], line 1
----> 1 bool(foo>Integer(0))

File /usr/local/sage-10/src/sage/symbolic/expression.pyx:3453, in sage.symbolic.expression.Expression.__bool__()
   3451 pynac_result = decide_relational(self._gobj)
   3452 if pynac_result == relational_undecidable:
-> 3453     raise ValueError('undecidable relation: ' + repr(self))
   3454 
   3455 # pynac is guaranteed to give the correct answer for comparing infinities

ValueError: undecidable relation: Infinity > 0

HTH,