Added a couple of utility methods useful at my end but which seemed to belong in BMT

[RichardBruskiewich]

• is_symmetric() - tests (predicate) element symmetry
• get_inverse_predicate() - a bit more thorough than get_inverse()

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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