0c is not accepted for parameters, but only in the form 0*c

[gorzel]

For parameters, unlike variables, an input in the form 0c is not accepted.

> ring rc0 =(0,c),x,dp;
> setring rc0;
> 2x;
2*x
> 0x;    // OK
0
> 2c;    // OK
(2c)
> 0c;   // Bug here
   ? `0c` is undefined
   ? error occurred in or before STDIN line 23: `0c;`
> 0*c;       // the * should not be required
0

Certainly, nobody wants to write explicitely something like "0cx" but the problem is that reduction of equations modulo a prime number will lead to such terms.

> ring rc5 = (5,c),x,dp;
> 5x;
0
> 5c;
   ? `5c` is undefined
   ? error occurred in or before STDIN line 27: `5c;`
> 5*c;
0

[hannes]

The * may only be omitted for monomials. For example (in the setting above), 3c is a (constant monomial), while 5c is not.