ON CONSTRUCTIONS OF SOME CLASSES OF QUASI-HEREDITARY ALGEBRAS

Inspired by the work of Mirollo and Vilonen [MV] describing the catego ries of perverse sheaves as module categories over certain finite dime nsional algebras, Dlab and Ringel introduced [DR2] an explicit recursi ve construction of these algebras in terms of the algebras A(gamma). I n particular, they characterized the quasi-hereditary algebras of Clin e-Parshall-Scott [PS] and constructed them in this way. The present pa per provides a characterization of lean algebras and some other specia l classes of algebras in terms of this recursive process.