C0[p10, p12, p20, m1^2, m2^2, m3^2] is the scalar
Passarino-Veltman C_0 function. The
convention for the arguments is that if the denominator of the integrand
has the form ([q^2-m1^2] [(q+p1)^2-m2^2]
[(q+p2)^2-m3^2]), the first three arguments of C0 are the scalar
products p10 = p1^2, p12 = (p1-p2).(p1-p2), p20 = p2^2.
Overview, B0, D0, PaVe, PaVeOrder.
C0[a, b, c, m12, m22, m32]\text{C}_0(a,b,c,\text{m12},\text{m22},\text{m32})
C0[b, a, c, m32, m22, m12] // PaVeOrder\text{C}_0(a,b,c,\text{m12},\text{m22},\text{m32})
PaVeOrder[C0[b, a, c, m32, m22, m12], PaVeOrderList -> {c, a}]\text{C}_0(c,a,b,\text{m32},\text{m12},\text{m22})