[ Eq(x10, x1 + x3),
  Eq(x11, x2 + x4),
  Eq(x12, x8 + x3 + x4),
  Eq(x15, x13 + x14),
  Eq(x16, x7 + x13 + x14),
  Eq(x17, x9 + x13),
  Eq(x18, x9 + x6 + x13 + x14),
  Eq(1*k27*x6 + 1*k27*x9 + 1*k27*x13 + 1*k27*x14, k27*k28) ]