What are the lines of the Philidor Defence?
To start: White moves this pawn forward
Black mirrors by moving this pawn
White moves his Knight
Black puts his pawn here
Then White moves this pawn
This is the Main line of the Philidor Defence
If Black replies by moving the Knight
This is the Hanham Variation
If Black takes this pawn instead...
This is the Exchange Variation
But if Black replies by moving the Knight
This is the Nimzowitsch Variation