1 | initial version |

To expand on the comment by @kcrisman, limits are sent to maxima by default. Maxima can evaluate the limit of the step function: entering

```
unit_step(x).limit(x=0,dir='right')
```

returns `1`

as expected. Maxima cannot evaluate the limit of the Dirac delta: entering

```
dirac_delta(x).limit(x=0,dir='right')
```

returns an unevaluated expression. Since part of your limit cannot be evaluated by Maxima, it all comes back unevaluated.

The other option for limit evaluation is to set `algorithm='sympy'`

: entering

```
dirac_delta(x).limit(x=0,algorithm='sympy')
```

returns zero as expected. Unfortunately, entering

```
dirac_delta(x).limit(x=0,dir='right',algorithm='sympy')
```

gives the message

```
sympy does not support one-sided limits
```

Even more problematic, entering

```
unit_step(x).limit(x=0,algorithm='sympy')
```

gives the message

```
SymPy function 'unit_step' doesn't exist
```

so SymPy won't get the complete job done either.

Not exactly the answer you want, but hopefully it helps you understand what's happening.

2 | No.2 Revision |

To expand on the comment by @kcrisman, limits are sent to ~~maxima ~~Maxima by default. Maxima can evaluate the limit of the step function: entering

```
unit_step(x).limit(x=0,dir='right')
```

returns `1`

as expected. Maxima cannot evaluate the limit of the Dirac delta: entering

```
dirac_delta(x).limit(x=0,dir='right')
```

returns an unevaluated expression. Since part of your limit cannot be evaluated by Maxima, it all comes back unevaluated.

The other option for limit evaluation is to set `algorithm='sympy'`

: entering

```
dirac_delta(x).limit(x=0,algorithm='sympy')
```

returns zero as expected. Unfortunately, entering

```
dirac_delta(x).limit(x=0,dir='right',algorithm='sympy')
```

gives the message

```
sympy does not support one-sided limits
```

Even more problematic, entering

```
unit_step(x).limit(x=0,algorithm='sympy')
```

gives the message

```
SymPy function 'unit_step' doesn't exist
```

so SymPy won't get the complete job done either.

Not exactly the answer you want, but hopefully it helps you understand what's happening.

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