1. Institute of Computer Science Academy of Sciences of the Czech Republic Pod Vodárenskou věží 2, 182 07 Prague 8 Czech Republic
2. Department of Mathematics and Applied Mathematics University of Pretoria Private Bag X20, Hatfield Pretoria 0028 South Africa
3. DST‐NRF Centre of Excellence in Mathematical and Statistical Sciences (CoE‐MaSS) 1 Jan Smuts Avenue, Braamfontein 2000 Johannesburg South Africa