{ diff(x1, t) = ((-1)*k15*k1*x1*x11*(1 + (x11/k2)^k3)^(-1) + 1*k15*k10)/k15,
  diff(x2, t) = ((-1)*k16*k1*x2*x12*(1 + (x12/k2)^k3)^(-1) + 1*k16*k10)/k16,
  diff(x3, t) = (2*k15*k1*x1*x11*(1 + (x11/k2)^k3)^(-1) + (-1)*k15*k4*x3*x16 + (-1)*k15*k8*x3*x9)/k15,
  diff(x4, t) = (2*k16*k1*x2*x12*(1 + (x12/k2)^k3)^(-1) + (-1)*k16*k4*x4*x17 + (-1)*k16*k8*x4*x10)/k16,
  diff(x5, t) = (1*k15*k4*x3*x16 + (-1)*k15*k5*x5*x18)/k15,
  diff(x6, t) = (1*k16*k4*x4*x17 + (-1)*k16*k5*x6*x19)/k16,
  diff(x7, t) = (1*k15*k5*x5*x18 + (-1)*k15*k6*x7*x9 + (-1)*k15*k13*(x7 - x13))/k15,
  diff(x8, t) = (1*k16*k5*x6*x19 + (-1)*k16*k6*x8*x10 + (-1)*k16*k13*(x8 - x13))/k16,
  diff(x9, t) = (1*k15*k4*x3*x16 + (-1)*k15*k6*x7*x9 + (-1)*k15*k8*x3*x9)/k15,
  diff(x10, t) = (1*k16*k4*x4*x17 + (-1)*k16*k6*x8*x10 + (-1)*k16*k8*x4*x10)/k16,
  diff(x11, t) = ((-2)*k15*k1*x1*x11*(1 + (x11/k2)^k3)^(-1) + 2*k15*k5*x5*x18 + (-1)*k15*k7*x11)/k15,
  diff(x12, t) = ((-2)*k16*k1*x2*x12*(1 + (x12/k2)^k3)^(-1) + 2*k16*k5*x6*x19 + (-1)*k16*k7*x12)/k16,
  diff(x13, t) = ((-1)*k17*k9*x13 + 1*k17*k14/2*(k13*(x7 - x13) + k13*(x8 - x13)))/k17,
  diff(x14, t) = 0,
  diff(x15, t) = 0 }