1 | initial version |

I think I know what happened. I don't know if it should be considered user error or a bug.

Look at the code in question.

```
sage: [u02-1]
[u02 - 1]
sage: isinstance(u02-1,tuple)
False
sage: isinstance(u02-1,list)
False
sage: function_type=type(lambda x,y: x+y)
sage: function_type
<type 'function'>
sage: isinstance(u02-1,function_type)
False
```

And clearly it's not `None`

, so the if/elif never actually gives `min`

a value. Also notice that all the examples use lambda functions for their `cons`

values.

Since `cons`

"This should be either a function or list of functions that must be positive", perhaps just having a symbolic expression is not enough. After all, who knows what the variable is to be? But maybe we should have a better error check for this?

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