Hi all!
There appears to be a bug involving block orders. The equality for
TermOrder does not take lengths into account, so two different block
orderings are considered equal. As a result, trying to change the block
sizes of a polynomial ring has no effect, as the ring is cached.
sage: R = PolynomialRing(QQ, 6, 'x', order="lex(1),lex(5)")
sage: S = R.change_ring(order="lex(2),lex(4)")
sage: R.term_order() != S.term_order()
False
sage: R is S
True
sage: TermOrder("lex(1),lex(5)") == TermOrder("lex(2),lex(4)")
True
Although the source code for TermOrder mentions that lengths are not
considered for equality, this seems to be incorrect behaviour in case of
block orderings.
I am using Sage 8.1 on OS X 10.13.
Markus
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