def is_variable(b):
    return isinstance(b, str) and b.isupper()

def unify(ctx, a, b):
    """
    a is the more specific type
    b is the type with parameter
    lower case means primitive type
    upper case means type variable
    list and tuples are just list and tuples
    """
    if isinstance(ctx, str):
        return ctx

    if is_variable(b):
        if b in ctx:
            b = ctx[b]
        else:
            ctx[b] = a
            return ctx
    else:
        if is_variable(a):
            return f"{a} is less specific then {b}"

    if isinstance(a, list) and isinstance(b, list):
        return unify(ctx, a[0], b[0])
    elif isinstance(a, tuple) and isinstance(b, tuple) and len(a) == len(b):
        old = ctx
        for x, y in zip(a, b):
            old = unify(old, x, y)
        return old
    else:
        if a == b:
            return ctx
        else:
            return f"{a} != {b}"

def check_eq(a, b):
    unifier = unify({}, a, b)
    print(f"{a} <- {b}\n{unifier}\n")

check_eq('a', 'A')
check_eq('A', 'B')
check_eq('A', 'a')
check_eq(['a'], 'A')
check_eq(['a'], ['A'])
check_eq(['a'], ['b'])
check_eq([('a', 'a', 'b')], ['A'])
check_eq([('a', 'a', 'b')], [('A', 'A', 'B')])
check_eq([('a', 'a', 'b')], [('A', 'A', 'A')])