Roleset dwindle.01 Verbnet Class: NONE "become less":

Roles:

Arg1:thing becoming less


Arg2:EXT or MNR


Arg3:start point


Arg4:end point

Examples:

person: ns tense: past aspect: ns voice: active form: full


just unaccusative intransitive (-)
That's largely because of defensive measures they adopted after the 1987 crash, when individual investors fled the market and trading activity dwindled *trace*.
Arg1:	trading activity
REL:	dwindled
ArgM-TMP:	*trace* -> when -> the 1987 crash

I'm predicting the numeric arguments, but they might not actually occur.