Properties of form `has_invX_equals_invY` do not handle precision errors

[yirkajk]

For example,

Graph(1).lovasz_theta()
independence_number(Graph(1))
has_lovasz_theta_equals_alpha(Graph(1))

yields

0.99999999
1
False

[math1um]

What to do in this common case? The issue, of course, is numerical methods.

Maybe the best thing here is to declare (possibly wrongly) that we have equality if the difference is relatively small, say no more than 10^{-6}? (We'll probably get more false negatives if we don't round, than false positives from allowing an error tolerance).