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List partitions generalize list colourings and list homomorphisms. Each symmetric matrix M over 0; 1; deenes a list partition problem. Diierent choices of the matrix M lead to many well-known graph the-oretic problems including the problem of recognizing split graphs and their generalizations, nding homogeneous sets, joins, clique cutsets, stable cutsets,(More)
We introduce a parametrized family of graph problems that includes several well-known graph partition problems as special cases. We develop tools which allow us to classify the complexity of many problems in this family, and in particular lead us to a complete classiication for small values of the parameters. Along the way, we obtain a variety of speciic(More)
The comparative analysis of Ig class switch recombination in a priori IgG/IgA-expressing myelomas and hybridomas, in switch variants and in activated normal B cells shows the following characteristics of class switch recombination in activated B cells: It is prevented during most of B cell ontogeny. It happens on both IgH loci of activated and switched B(More)
Immunoglobulin (Ig) gene promotors are active only in cells of the B-lymphocyte lineage. Transfection experiments have shown that this is due in part to tissue specific 'activating' DNA sequences, so called enhancers. It is not entirely clear whether these sequences are necessary for initial activation or also for maintenance of transcription of a gene. We(More)
A transcriptional enhancer is thought to play a major role in determining tissue-specific expression of the immunoglobulin heavy chain (IgH) gene (1-3). However in three B-lymphoid cell lines the Ig enhancer has been lost due to a spontaneous deletion, yet heavy chain synthesis persists at a high level (4-6). In the case of the enhancerless delta chain gene(More)
We consider the following generalization of split graphs: A graph is said to be a (k, ℓ)-graph if its vertex set can be partitioned into k independent sets and ℓ cliques. (Split graphs are obtained by setting k = l = 1). Much of the appeal of split graphs is due to the fact that they are chordal, a property not shared by (k, ℓ)-graphs in general. (For(More)
A skew partition as defined by Chvátal is a partition of the vertex set of a graph into four nonempty parts AA BB CC D such that there are all possible edges between A and B and no edges between C and D. We present a polynomial-time algorithm for testing whether a graph admits a skew partition. Our algorithm solves the more general list skew partition(More)
A homogeneous set is a non-trivial module of a graph, i.e. a non-empty, non-unitary, proper subset of a graph's vertices such that all its elements present exactly the same outer neighborhood. Given two published an all-fast O(n 2 2) algorithm which was recently proven wrong [5], so that the HSSP's known upper bound would have been reset thereafter at(More)