code: def dmp_sub(f, g, u, K):
      """
      Subtract dense polynomials in ``K[X]``.
  
      Examples
      ========
  
      >>> from sympy.polys import ring, ZZ
      >>> R, x,y = ring("x,y", ZZ)
  
      >>> R.dmp_sub(x**2 + y, x**2*y + x)
      -x**2*y + x**2 - x + y
  
      """
      if not u:
          return dup_sub(f, g, K)
  
      df = dmp_degree(f, u)
  
      if df < 0:
          return dmp_neg(g, u, K)
  
      dg = dmp_degree(g, u)
  
      if dg < 0:
          return f
  
      v = u - 1
  
      if df == dg:
          return dmp_strip(
              [dmp_sub(a, b, v, K) for a, b in zip(f, g)], u
          )
      else:
          k = abs(df - dg)
  
          if df > dg:
              h, f = f[:k], f[k:]
          else:
              h, g = dmp_neg(g[:k], u, K), g[k:]
  
          return h + [dmp_sub(a, b, v, K) for a, b in zip(f, g)]
  
imports: from sympy.polys.densebasic import dup_slice, dup_LC, dmp_LC, dup_degree, dmp_degree, dup_strip, dmp_strip, dmp_zero_p, dmp_zero, dmp_one_p, dmp_one, dmp_ground, dmp_zeros
  from sympy.polys.polyerrors import ExactQuotientFailed, PolynomialDivisionFailed
label_desc: Use image node_id 26 for calling a global function with example usage: dmp_sub(f, g, u, K) and returns: dup_sub, dmp_neg, f, dmp_strip, unknown