I try to define the Multiplication-Operation for a Group/Ring but I can for example not write “*: MxM->M”, because Math interprets * as an operator. How can I add a symbol and escape its semantics?

- You can add the symbol to the catalog and later use it with %. Read the Math-Guide from https://wiki.documentfoundation.org/Documentation/Publications how to do that.
- You can tread the symbol as text and write “*”, e.g.
`"* : "M times M rightarrow M`

- You can treat the symbol as operator - which it is in your case - and write it with empty operands. An empty operand can be written as empty group {}. In your case write
`{}*{}": "M times M rightarrow M`