Define as the minimum operations to convert A[0..i-1] to B[0..j-1]. Base cases differ from LCS: : Converting empty string to B[0..j] requires insertions. : Converting A[0..i] to empty string requires deletions.
These non-zero base cases reflect that converting to/from empty strings has a cost. Unlike LCS, base cases here are non-zero: converting to or from an empty string costs exactly the other string's length.