code: def test_subtract():
      x, y, z = (F.Term(l) for l in "xyz")
      f1 = F.Formula([x, y])
      f2 = F.Formula([x, y, z])
      f3 = f2 - f1
      assert set(f3.terms) == {z}
      f4 = F.Formula([y, z])
      f5 = f1 - f4
      assert set(f5.terms) == {x}
  
imports: from warnings import catch_warnings, simplefilter
  import numpy
  import pytest
  import sympy
  from numpy.core.records import fromrecords
  from numpy.testing import assert_almost_equal, assert_array_equal
  from sympy.utilities.lambdify import implemented_function
  from nipy.utils import VisibleDeprecationWarning
  from ..None import formulae
  from ..formulae import Term, terms
label_desc: Use image node_id 27 for calling a global function with example usage: test_subtract() without return types