How to Customize Sigma in subexpr()?

Let's say we have a formula below

syms k1 k2
eqn2 = (k1+k2+1)^2+(k1+k2+1)+1;

and put 'eqn2' into subexpr() function,

[EQN2, sigma] = subexpr(eqn2)

then the answer would be as follows:

EQN2 = sigma^2 + sigma + 1
sigma = k1 + k2 + 1

However, this time, I would like the sigma to be k1 + k2.

Could I customize the sigma as I want? If it's yes, how could I replace it?

Answer 1

[madhan ravi]

subs(eqn2,sigma,k1+k2)

[Aoi Midori]

Thank you for your quick response. It worked!