C5W1A1 Exercise7. What is this: d_gamma_c?

At equation (17), to calculate dbc, it says I have to sum d_gamma_cs, but there is no d_gamma_c throughout the whole assignment except for that part.
It somehow worked using dcct in the code, which is dpc_tilde in formula (8).
Is this just a typo? Or am I missing something from the lecture or descriptions?

I guess you are right. It’s a typo. The below screenshot confirms it. Thanks for reporting it.