18. Means according to claim 17 wherein said means for further processing comprises: means for merging the textual block identifiers taken from different ones of said further groups of textual block identifiers without duplicating therein any of the same textual block identifiers; and the means for processing comprises means for forming a representation of a score for each a plurality of the textual blocks, each said representation of a score indicating the number of further groups which contain at least one of the textual block identifiers corresponding to such textual block.
17. Means according to claim 13 wherein the means for processing comprises: means for merging the textual block identifiers in the groups corresponding to the equivalent words in the sets of equivalent words into a further group of textual block identifiers, one of said further groups of textual block identifiers being formed for each set of equivalent words without duplicating therein any of the same textual block identifiers; and means for further processing each said further group of textual block identifers to thereby form said representation of a score.