Sample Problem
For someone (call him or her X) to be the grandmother of someone else (call him or her Y), X must be the mother of someone (call him or her Z) who is a parent of Y.
Someone is a parent of another person, if that someone is either the mother or the father of the other person.
Mary is the mother of Stan.
Gwen is the mother of Alice.
Valery is the mother of Gwen.
Stan is the father of Alice.
The question: Who is a grandmother of Alice?