> The other part where I'm stuck is the function
>
> rows(A:M, si:SPI) : M
> )show Segment
> ...
> expand : % -> List(S) if S has ORDRING
And there lies the reason for why your code does not compile.
The following works, but is (of course) not the right solution.
rows(A:M, si:SPI) : M ==
rows(A, (expand(si pretend Segment(Integer))$Segment(Integer))
pretend List(PI))
> (1) -> PI has ORDRING
>
> (1) false
> This means I can not expand a Segment(PI) into a List?
Exactly.
> Why not, it seems to be a natural operation, no?
Right, but the current library implementation is unnecessarily restrictive.
I guess for "expand" we only need OrderedSet, a distinct element 1
(default step size) and an operation +. In fact, disregarding the "by"
construction of a segment, a function next: %->% would be enough.
Anyway, the current implementation gets the 1 and + from OrderedRing.
So without changing the library you would have to locally implement
"expand" for Segment(PositiveInteger)
Take a look at
https://github.com/hemmecke/fricas/blob/master/src/algebra/seg.spad.pamphlet#L150
and modify the respective types for your local myexpand: SPI -> LPI
function.
Ralf
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