Problem:
LatticePoset({'a':['b', 'c'], 'b':['d', 'e'], 'c':['d', 'e'],
'd':['f'], 'e':['f']})
returns "ValueError: Not a lattice." I would like to see for example "Not
a lattice: no meet for e and d."
Solution: From hasse_diagram.py do not raise just "no meet for x=1 y=2"
but exception with value more complicated than a string.
Question: Will this break something? I.e. can "internal" classes raise
these kind of exceptions?
Example implementation: http://trac.sagemath.org/ticket/19163 . NOT in
needs_review yet.
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Jori Mäntysalo
