Should the XARG or INDEX of an adjective's SPR to be linked to its INDEX?

Grammar Matrix
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1

Side story: I’ve just released the in-progress Kalaallisut grammar as the coverage on the collected 1500-sentence corpus has reached 25%. See here: GitHub - alexhsu-nlp/kal-hpsg: An HPSG grammar fragment of Kalaallisut (West Greenlandic).

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Adjectives in the Grammar Matrix has the following supertype in matrix.tdl:

basic-adjective-lex := norm-sem-lex-item &
  [ SYNSEM [ LOCAL [ CAT [ HEAD adj,
                           VAL [ COMPS < >,
                                 SPEC < >,
                                 SPR.FIRST.LOCAL [ CAT.HEAD adv,
                           CONT.HOOK.XARG #index ] ] ] ],
             LKEYS.KEYREL event-relation &
                    [ ARG0 #index ] ] ].

However, basic-head-spec-phrase says the following:

basic-head-spec-phrase := basic-head-spec-phrase-super &
  [ NON-HEAD-DTR.SYNSEM.LOCAL.CONT.HOOK #hook,
    C-CONT.HOOK #hook ].

This means that the CONT value of the projected phrase will be the same as that of the specifier’s. Therefore, if we, for example, want the XARG of a predicate adjective to still refer to the subject waiting to be combined, the XARG of the specifier must be the same as the XARG of the adjective, not its event INDEX.

Is this a bug of matrix.tdl? My current refactoring in the released grammar is as follows:

base-basic-adj-lex := norm-sem-lex-item &
  [ SYNSEM [ LOCAL [ CAT [ HEAD adj,
                           VAL [ COMPS < >,
                                 SPEC < > ] ] ] ] ]
"""The base type of common adjectives and numerals""".

basic-adjective-lex := base-basic-adj-lex &
  [ SYNSEM [ LOCAL [ CAT [ VAL.SPR.FIRST.LOCAL [ CAT.HEAD adv,
                                                 CONT.HOOK.INDEX #index ] ] ],
             LKEYS.KEYREL event-relation & [ ARG0 #index ] ] ]
"""The base type of non-numeral adjectives. These adjectives can take a degree specifier.""".

And it seems that after making the specifier’s INDEX to be identified with the adjective’s INDEX instead, the MRS for a predicate adjective taking a numeral degree specifier (the closest English counterpart is like “it is 15cm long”) finally looks like the one from the ERG 2018 demo.