Fixed mistake in doc. Added is_numeric property for variables

docs/conceptual_guide.md

@@ -284,7 +284,7 @@ The complement of a simple event is given by
 
 ```{math}
 :label: eq-complement-product-sigma-algebra
-(A \times B)^c = (A^c \times B) \cup (A \times B) \cup (A \times B^c). 
+(A \times B)^c = (A^c \times B) \cup (A \times B^c) \cup (A^c \times B^c). 
 ``` 
 {cite}`hunter2011data`
 ````

src/random_events/variable.py

@@ -1,6 +1,8 @@
+from abc import abstractmethod
+
 from typing_extensions import Self, Type, Dict, Any, Union, Optional
 
-from .interval import Interval, SimpleInterval, reals
+from .interval import Interval, reals
 from .set import Set, SetElement
 from .sigma_algebra import AbstractCompositeSet
 from .utils import SubclassJSONSerializer
@@ -49,6 +51,14 @@ def to_json(self) -> Dict[str, Any]:
     def _from_json(cls, data: Dict[str, Any]) -> Self:
         return cls(data["name"], AbstractCompositeSet.from_json(data["domain"]))
 
+    @property
+    @abstractmethod
+    def is_numeric(self):
+        """
+        :return: Rather, this variable has a numeric domain or not.
+        """
+        raise NotImplementedError
+
 
 class Continuous(Variable):
     """
@@ -61,6 +71,10 @@ class Continuous(Variable):
     def __init__(self, name: str, domain=None):
         super().__init__(name, reals())
 
+    @property
+    def is_numeric(self):
+        return True
+
 
 class Symbolic(Variable):
     """
@@ -93,6 +107,10 @@ def __init__(self, name: Optional[str] = None, domain: Union[Type[SetElement], S
     def domain_type(self) -> Type[SetElement]:
         return self.domain.simple_sets[0].all_elements
 
+    @property
+    def is_numeric(self):
+        return False
+
 
 class Integer(Variable):
     """
@@ -104,3 +122,7 @@ class Integer(Variable):
 
     def __init__(self, name: str, domain=None):
         super().__init__(name, reals())
+
+    @property
+    def is_numeric(self):
+        return True