There is nothing complicated about the ending -uf (or -um ....) for direction.

Peter sidijt na stul. (Peter is sitting on a chair.)
Peter sidijt na stuluf. (Peter is sitting down on a chair.) (Direction)

Peter idijt v sxkol. (Peter is walking inside school.)
Peter idijt v sxkoluf. (Peter is walking towards school.) (Direction.)

Peter idijt na gora. (Peter is walking on a mountain.)
Peter idijt na goraf. (Peter is going onto a mountain.) (Direction)

Peter sberijt gribis v les. (Peter is picking mushrooms in a forest.)
Peter bu idit sberit gribis v lesuf. (Peter will go to pick mushrooms into a forest.) (direction)

except for the fact that nobody but Slovio scholars understand the distinction

In Russian we have:

on idet v Moskve -- where?
on idet v Moskvu -- to where?

on idet v lesu -- where?
on idet v les -- to where?

As you see in one case -u ending tells where the action takes place, and in other case -u ending tells us to where the direction of the action is.

So I doubt such distinguishing a is good idea.

Or, let's approach the problem from other side:

In Russian:

V lesu -- where?
V les -- to where?

In Slovio:

V les -- where?
V lesuf -- to where?

Or, let's approach the problem from other side:

In Russian:

V lesu -- where?
V les -- to where?

In Slovio:

V les -- where?
V lesuf -- to where?
=====================================


NOW I understand why I didn't understand

Good.

So how do you propose to solve this situation in a schematic language? Of course, in a naturalistic one, you will use locative for the meaning "where" and accussative for the meaning "to where". Similarly, German uses dative for the meaning "where" and accussative for the meaning "to where". In a schematic language, I think that nominative for "where" and accussative for "to where" is a good replacement, as used in Esperanto and Slovio.

In a schematic language, I think that nominative for "where" and accussative for "to where" is a good replacement

I don't know what about you guys, but the fact that languages like German use almost the same solution of "whither" problem as Russian doesn't help me at all. When I write in German I have to keep in mind this "wodat-wohinak" rule (Wo? -- Dativ; Wohin? -- Akkusativ) For some reason such cases are very confusable for me (though I don't have Dat/Akk destinguishing problems in other situations).

Best solution I think is using either of different verbs (like in GS-Slovio) or of different prepositions (na/po vs. k/do)

By the way, when I was a university student and I had to write up the lections, I used a very complicated system of abbreviations, totally excluding the using of any endings -- it caused the where/whither problem. To overcome it, I started to mark prepostions with special symbols: "^:" for "whither" prepositions, and something like "^U" for "where" ones. It looked something like this: "ÿ æèâ^{I U}â Ðñ^/" -- "I live in Russia"; "ß íèêäà íå ïèåä^{I :}â Ìñêâ" -- "I won't ever come to Moscow".

Interesting ... When I learned German, I had problems to remember the form of the article, the gender of the concerned noun, the correct ending for the corresponding adjective - but I have never had any problem to distinct dative/accussative for where/whither.

But never mind. I just think that there should be some way to express the direction; not to have it might be easy for the active user, but very difficult to understand.

Gabriel:
So how do you propose to solve this situation in a schematic language? Of course, in a naturalistic one, you will use locative for the meaning "where" and accussative for the meaning "to where". Similarly, German uses dative for the meaning "where" and accussative for the meaning "to where". In a schematic language, I think that nominative for "where" and accussative for "to where" is a good replacement, as used in Esperanto and Slovio.
===
Gabriel es korekt. No to znacit zxe Slovio imat cxtir padesx takak Nemcio:

1.Nominativ
postel
2.Genitiv
detevoi postel
3.Dativ
Dete skacxit vo postel
4.Akuzativ
Dete skacxit vo postelum

Ocxviduo, Zamenhof gvoril i Hucxko gvorit Nemcju jazika.

Every language has to be able to express these four cases. Or how do you propose to get rid of them?

upotrebit Anglio ili Bulgario!

According to your logic, English has got these cases, too:

nominative: a bed
genitive: a child's bed
dative: a child jumps on a bed
accusative: a child jumps onto a bed

Yes, cases can be replaced by prepositions or word order, as done in English or Slovio. Not every language has to have these cases, but every language, including Slovio, has to have ways to express them.

All cases are replaced by prepositions or word order

Yes, both in English and in Slovio, so I don't know what you are complaining about.

I am not complaining, it was you who defended Slovio´s dative and accusative case. By the way I like Slovio´s genetive (which is almost dead in English and does no more exisist in Southgerman language) and subject/object case.

Gabriel:
Every language has to be able to express these four cases. Or how do you propose to get rid of them?
===

Kto to pisal?
" Cases: All cases are replaced by prepositions or word order."