diff --git a/nmigen/__init__.py b/nmigen/__init__.py
index 473e8de..88596a5 100644
--- a/nmigen/__init__.py
+++ b/nmigen/__init__.py
@@ -1,4 +1,4 @@
-from .hdl.ast import Value, Const, C, AnyConst, AnySeq, Mux, Cat, Repl, Array, Signal, ClockSignal, ResetSignal, Assert, Assume
+from .hdl.ast import Value, Const, C, Mux, Cat, Repl, Array, Signal, ClockSignal, ResetSignal
 from .hdl.dsl import Module
 from .hdl.cd import ClockDomain
 from .hdl.ir import Fragment, Instance
diff --git a/nmigen/formal.py b/nmigen/formal.py
new file mode 100644
index 0000000..3d97b33
--- /dev/null
+++ b/nmigen/formal.py
@@ -0,0 +1 @@
+from .hdl.ast import AnyConst, AnySeq, Assert, Assume