diff --git a/src/dofs/mixed.jl b/src/dofs/mixed.jl
deleted file mode 100644
index 11bf6a9..0000000
--- a/src/dofs/mixed.jl
+++ /dev/null
@@ -1,95 +0,0 @@
-# This file is a part of JuliaFEM.
-# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE
-
-"""
-Mixed DOF Types - Entity-Based
-
-Implementation of mixed/coupled DOF systems where multiple DOF types
-coexist on the same element.
-
-# Core Type
-
-- `MixedDOF{DOFs}`: Composition of multiple entity-based DOF types
-
-# Use Cases
-
-**Stokes (velocity + pressure):**
-```julia
-MixedDOF{(
-    DOF{Vec{2}, Vertex{Triangle{3}}},    # Velocity at vertices
-    DOF{Float64, Vertex{Triangle{3}}}    # Pressure at vertices
-)}
-```
-
-**3-Field Formulation (u + p + J):**
-```julia
-MixedDOF{(
-    DOF{Vec{3}, Vertex{Tetrahedron{4}}},    # Displacement at vertices
-    DOF{Float64, Vertex{Tetrahedron{4}}},   # Pressure at vertices
-    DOF{Float64, Edge{Tetrahedron{4}}}      # Volumetric DOF on edges
-)}
-```
-
-**Mixed Interpolation (Taylor-Hood):**
-```julia
-MixedDOF{(
-    DOF{Vec{2}, Vertex{Triangle{6}}},    # Quadratic velocity
-    DOF{Float64, Vertex{Triangle{3}}}    # Linear pressure (different topology!)
-)}
-```
-
-# DOF Ordering
-
-Mixed DOFs are concatenated in order:
-```julia
-MixedDOF{(DOF{Vec{2}, Vertex{Triangle{3}}}, DOF{Float64, Vertex{Triangle{3}}})}
-# For Triangle{3}:
-# Field 1: [u1x, u1y, u2x, u2y, u3x, u3y]  (6 DOFs from 2×3 vertices)
-# Field 2: [p1, p2, p3]                     (3 DOFs from 1×3 vertices)
-# Total:   [u1x, u1y, u2x, u2y, u3x, u3y, p1, p2, p3]  (9 DOFs)
-```
-
-"""
-
-# MixedDOF is already defined in api.jl, this file adds helper functions
-
-# ============================================================================
-# Helper Functions
-# ============================================================================
-
-"""
-Check if DOF type is mixed.
-"""
-is_mixed(::Type{<:MixedDOF}) = true
-is_mixed(::Type{<:DOF}) = false
-
-"""
-Get the tuple of constituent DOF types.
-"""
-function get_dof_types(::Type{MixedDOF{DOFs}}) where {DOFs}
-    return DOFs.parameters
-end
-
-"""
-Get number of fields in mixed system.
-"""
-function num_fields(::Type{MixedDOF{DOFs}}) where {DOFs}
-    return length(DOFs.parameters)
-end
-
-"""
-Get DOF type for specific field (1-indexed).
-"""
-function get_field_dof_type(::Type{MixedDOF{DOFs}}, field_idx::Int) where {DOFs}
-    return DOFs.parameters[field_idx]
-end
-
-# ============================================================================
-# Display
-# ============================================================================
-
-function Base.show(io::IO, ::Type{MixedDOF{DOFs}}) where {DOFs}
-    dof_types = [string(T) for T in DOFs.parameters]
-    print(io, "MixedDOF{(", join(dof_types, ", "), ")}")
-end
-