diff --git a/pyk/src/pyk/kore/internal.py b/pyk/src/pyk/kore/internal.py
new file mode 100644
index 0000000000..4eda572da2
--- /dev/null
+++ b/pyk/src/pyk/kore/internal.py
@@ -0,0 +1,134 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, final
+
+from ..utils import FrozenDict, POSet
+from .manip import collect_symbols
+from .rule import FunctionRule, RewriteRule, Rule
+from .syntax import App, Axiom, SortApp, SortDecl, Symbol, SymbolDecl
+
+if TYPE_CHECKING:
+    from .syntax import Definition
+
+
+@final
+@dataclass(frozen=True)
+class KoreDefn:
+    sorts: FrozenDict[str, SortDecl]
+    symbols: FrozenDict[str, SymbolDecl]
+    subsorts: FrozenDict[str, frozenset[str]]
+    rewrites: tuple[RewriteRule, ...]
+    functions: FrozenDict[str, tuple[FunctionRule, ...]]
+
+    @staticmethod
+    def from_definition(defn: Definition) -> KoreDefn:
+        sorts: dict[str, SortDecl] = {}
+        symbols: dict[str, SymbolDecl] = {}
+        subsorts: list[tuple[str, str]] = []
+        rewrites: list[RewriteRule] = []
+        functions: dict[str, list[FunctionRule]] = {}
+
+        for sent in defn.sentences:
+            match sent:
+                case SortDecl(name):
+                    sorts[name] = sent
+                case SymbolDecl(Symbol(name)):
+                    symbols[name] = sent
+                case Axiom(attrs=(App('subsort', (SortApp(subsort), SortApp(supersort))),)):
+                    subsorts.append((subsort, supersort))
+                case Axiom():
+                    if Rule.is_rule(sent):
+                        rule = Rule.from_axiom(sent)
+                        if isinstance(rule, RewriteRule):
+                            rewrites.append(rule)
+                        elif isinstance(rule, FunctionRule):
+                            functions.setdefault(rule.lhs.symbol, []).append(rule)
+
+        return KoreDefn(
+            sorts=FrozenDict(sorts),
+            symbols=FrozenDict(symbols),
+            subsorts=POSet((supersort, subsort) for subsort, supersort in subsorts).image,
+            rewrites=tuple(rewrites),
+            functions=FrozenDict((key, tuple(values)) for key, values in functions.items()),
+        )
+
+    def let(
+        self,
+        *,
+        sorts: FrozenDict[str, SortDecl] | None = None,
+        symbols: FrozenDict[str, SymbolDecl] | None = None,
+        subsorts: FrozenDict[str, frozenset[str]] | None = None,
+        rewrites: tuple[RewriteRule, ...] | None = None,
+        functions: FrozenDict[str, tuple[FunctionRule, ...]] | None = None,
+    ) -> KoreDefn:
+        return KoreDefn(
+            sorts=self.sorts if sorts is None else sorts,
+            symbols=self.symbols if symbols is None else symbols,
+            subsorts=self.subsorts if subsorts is None else subsorts,
+            rewrites=self.rewrites if rewrites is None else rewrites,
+            functions=self.functions if functions is None else functions,
+        )
+
+    def project_to_symbols(self) -> KoreDefn:
+        """Project definition to symbols present in the definition."""
+
+        def _symbol_sorts() -> set[str]:
+            res = set()
+            for symbol_decl in self.symbols.values():
+                if isinstance(symbol_decl.sort, SortApp):
+                    res.add(symbol_decl.sort.name)
+                res.update(sort.name for sort in symbol_decl.param_sorts if isinstance(sort, SortApp))
+            return res
+
+        symbol_sorts = _symbol_sorts()
+
+        sorts: FrozenDict[str, SortDecl] = FrozenDict(
+            (sort, decl) for sort, decl in self.sorts.items() if sort in symbol_sorts
+        )
+        subsorts: FrozenDict[str, frozenset[str]] = FrozenDict(
+            (supersort, frozenset(subsort for subsort in subsorts if subsort in sorts))
+            for supersort, subsorts in self.subsorts.items()
+            if supersort in sorts
+        )
+        functions: FrozenDict[str, tuple[FunctionRule, ...]] = FrozenDict(
+            (function, rules) for function, rules in self.functions.items() if function in self.symbols
+        )
+
+        return self.let(
+            sorts=sorts,
+            subsorts=subsorts,
+            functions=functions,
+        )
+
+    def project_to_rewrites(self) -> KoreDefn:
+        """Project definition to symbols that are (transitively) referred to from rewrite axioms."""
+        rewrite_symbols = self._rewrite_symbols()
+        symbols: FrozenDict[str, SymbolDecl] = FrozenDict(
+            (symbol, decl) for symbol, decl in self.symbols.items() if symbol in rewrite_symbols
+        )
+        return self.let(symbols=symbols).project_to_symbols()
+
+    def _rewrite_symbols(self) -> set[str]:
+        """Return the set of symbols reffered to in rewrite rules."""
+        res = set()
+
+        # Symbols appearing in rewrite rules are relevant
+        pending = {
+            symbol for rewrite_rule in self.rewrites for symbol in collect_symbols(rewrite_rule.to_axiom().pattern)
+        }
+        while pending:
+            symbol = pending.pop()
+            if symbol in res:
+                continue
+
+            res.add(symbol)
+
+            # Symbols appearing in function rules of a releveant symbol are relevant
+            pending.update(
+                symbol
+                for function_rule in self.functions.get(symbol, ())
+                for symbol in collect_symbols(function_rule.to_axiom().pattern)
+            )
+
+        return res