Add class Axiom to model

pyk/src/pyk/k2lean4/model.py

@@ -49,6 +49,24 @@ class Declaration(Command, ABC):
     modifiers: Modifiers | None
 
 
+@final
+@dataclass
+class Axiom(Declaration):
+    ident: DeclId
+    signature: Signature
+    modifiers: Modifiers | None
+
+    def __init__(self, ident: str | DeclId, signature: Signature, modifiers: Modifiers | None = None):
+        ident = DeclId(ident) if isinstance(ident, str) else ident
+        object.__setattr__(self, 'ident', ident)
+        object.__setattr__(self, 'signature', signature)
+        object.__setattr__(self, 'modifiers', modifiers)
+
+    def __str__(self) -> str:
+        modifiers = f'{self.modifiers} ' if self.modifiers else ''
+        return f'{modifiers}axiom {self.ident} {self.signature}'
+
+
 @final
 @dataclass
 class Abbrev(Declaration):