1 | initial version |

To fix this, `a`

needs to be defined as the generator of `M`

.

The code in the question only sets `a`

as the display value for this generator.

So, do one of the following.

```
M.<a> = PolynomialRing(ZZ)
```

or

```
M.<a> = ZZ[]
```

or

```
M = PolynomialRing(ZZ, 'a')
a = M.gen()
```

or

```
M = PolynomialRing(ZZ, 'a')
M.inject_variables()
```

2 | No.2 Revision |

To fix this, `a`

needs to be defined as the generator of `M`

.

The code in the question only sets `a`

as the display value for this generator.

So, do one of the following.

```
M.<a> = PolynomialRing(ZZ)
```

or

```
M.<a> = ZZ[]
```

or

```
M = PolynomialRing(ZZ, 'a')
a = M.gen()
```

or

```
M = PolynomialRing(ZZ, 'a')
M.inject_variables()
```

Note that there is also a shortcut with `[[]]`

for defining a power series rings.

```
sage: M.<a> = ZZ[]
sage: M
Univariate Polynomial Ring in a over Integer Ring
sage: R.<x, y> = M[[]]
sage: R
Multivariate Power Series Ring in x, y over Univariate Polynomial Ring in a over Integer Ring
sage: f = a*x + y + x*y + O(x,y)^3
sage: f
a*x + y + x*y + O(x, y)^3
```

Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.