Is there any simple way of comparing UCA-conforming collations to determine if they are equal? I'm assuming that the table is visible and that the collating elements (ISO/IEC 14651 terminology for the items looked up in the collation element table) are the same. (Black box identification of the collation elements in finitely many steps is impossible.)
The first step is to check that collating elements sort in the same order, and with the same category of differences (I don't think there's a real theoretical difficulty there - I think spurious levels can be eliminated), but after that I'm floundering. All the nice algebraic properties are associated with the collation elements (the n-tuples of weights), not with the collating elements. For an example of algebraic nastiness, "a" < "ab", "bd" < "c", but "abd" > "abc". As an example with just two Thai characters, in DUCET 6.1.0, we have, amongst the collating elements: ก < เก < เ (<U+0E01> < <U+0E40, U+0E01> < <U+0E40>) The same applies in DUCET 6.2.0 (or at least, the current daft, Draft 9). However, when we add other strings, we get, for example: DUCET 6.1.0: ก < กเ <<< เก < เ (<U+0E01> < <U+0E01, U+0E40> <<< <U+0E40, U+0E01> < <U+0E40>) DUCET 6.2.0: ก < กเ = เก < เ (<U+0E01> < <U+0E01, U+0E40> = <U+0E40, U+0E01> < <U+0E40>) (The 4th level weights make a difference for the CLDR root collation to be called up by UCA 6.2.0!) I can produce a similar example with the Roman numerals U+2170 ROMAN NUMERAL ONE to U+2172 ROMAN NUMERAL THREE. In the comparison I'm planning to make, there will not be a 1-1 correspondence of weights. An algorithm (or approach) will be useful to me even if it requires that in the two collations the same collating element expands to the same number of non-null collation elements. (By null collation element, I mean elements such as [0000.0000.0000].) Richard.
