user: Question: What is the Byzantine Commander with a Bulgarian victory at the Siege of Lovech?
Columns: ['Battle', 'Date', 'Bulgarian Commander', 'Byzantine Commander', 'Result']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Battle of Ongal', '680', 'Asparukh', 'Constantine IV', 'Bulgarian victory']
SQL:

assistant: SELECT "Byzantine Commander" FROM "Table" WHERE "Result" = 'Bulgarian victory' AND "Battle" = 'Siege of Lovech';