Logic Resolution rule application

[gl0ck]

Homework Statement

Hi, there
there is one question, which I find it to be solvable, but the answer is that it cannot be solved.
Can someone explain me the answer given. I think there is a mistake on the underlined row, which leads to wrong answer.
I am not sure, so if someone can help me I will be very grateful!

Homework Equations

The Attempt at a Solution

 

[NascentOxygen]

i don't know this topic. But tracing back the pattern there seems an inconsequential typo, where that -d should be c. If you believe otherwise, please point out your reasoning and I'll take a closer look.

 

[gl0ck]

Thank you for the reply, that was the same thing I noticed, and this is the solution given by the lecturer, that is why I am asking.