Logarithmic pair

In algebraic geometry, a logarithmic pair consists of a variety, together with a divisor along which one allows mild logarithmic singularities. They were studied by .
Definition.
A boundary Q-divisor on a variety is a Q-divisor "D" of the form Σ"d""i""D""i" where the "D""i" are the distinct irreducible components of "D" and all coefficients are rational numbers with 0≤"d""i"≤1.
A logarithmic pair, or log pair for short, is a pair ("X","D") consisting of a normal variety "X" and a boundary Q-divisor "D".
The log canonical divisor of a log pair ("X","D") is "K"+"D" where "K" is the canonical divisor of "X".
A logarithmic 1-form on a log pair ("X","D") is allowed to have logarithmic singularities of the form
d log("z") = d"z"/"z" along components of the divisor given locally by "z"=0.