C78 Ruy Lopez

Code C78 covers Ruy Lopez lines after 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O in which Black avoids the quiet ...Be7. The Møller Defence, 5...Bc5, puts the king's bishop on the a7–g1 diagonal at once, aiming at f2. After 5...b5 6.Bb3, the Arkhangelsk Variation, 6...Bb7, brings the other bishop to the long diagonal to press on e4. The Neo-Arkhangelsk, 6...Bc5, develops the king's bishop actively instead. In all three, Black trades solidity for quick piece play and must meet White's standard plan of c3 and d4, which gains time against a bishop on c5.