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 | | In % addition, the information whether the list is empty, whether it has % exactly one element, and what is the abstraction of its head is % maintained. |
 | | More precisely, an abstract list is a quadruple % quad(nonempty:bool, oneelem:bool, hd:aelem, ord:order), where nonempty % tells us whether the list is nonempty, oneelem whether it has exactly % one element, and hd is the abstraction of the head. |
 | | The last field, % ord, basically gives information about the occurrence and order of % e1-elements and e2-elements in the list. |
| www.cs.yale.edu /homes/carsten/challenges/DFKI017.txt (840 words) |
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