Re: topological sort

> When I started to think of
> "count(...)=0" as a kind of a NOT, things became a bit clearer.  See
>below.

It's clearer still if you write it as not() rather than using count()


 field[count(type/ref)>0 and ... )

could more clearly be written


field[type/ref and ... )

and

field[count(type/ref)=0 or ...

could be written


field[not(type/ref) or ...


If you use a node set in a boolean contextthen it is true if it is non
empty, so it can be used directly rather than counting it and then
testing the value against 0.

David

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