Springer resolution

In mathematics, the Springer resolution is a resolution of the variety of nilpotent elements in a semisimple Lie algebra, or the unipotent elements of a reductive algebraic group, introduced by Tonny Albert Springer in 1969. The fibers of this resolution are called Springer fibers.
If "U" is the variety of unipotent elements in a reductive group "G", and "X" the variety of Borel subgroups "B", then the Springer resolution of "U" is the variety of pairs ("u","B") of "U"×"X" such that "u" is in the Borel subgroup "B". The map to "U" is the projection to the first factor. The Springer resolution for Lie algebras is similar, except that "U" is replaced by the nilpotent elements of the Lie algebra of "G" and "X" replaced by the variety of Borel subalgebras.
The Grothendieck–Springer resolution is defined similarly, except that "U" is replaced by the whole group "G" (or the whole Lie algebra of "G"). When restricted to the unipotent elements of "G" it becomes the Springer resolution.
Examples.
When "G=SL(2)", the Lie algebra Springer resolution is "T*P1 → n", where "n" are the nilpotent elements of "sl(2)". In this example, "n" are the matrices "x" with "tr(x2)=0", which is a two dimensional conical subvariety of "sl(2)". "n" has a unique singular point "0", the fibre above which in the Springer resolution is the zero section "P1 ".