numbersextensions functions in PMVector are perhaps better put in another place

[WernerK]

it would eventually make more sense to implement these methods in package numbersextensions on a lower level collection, have a look at eg Collection *Collections-arithmetic &
*Collections-arithmetic-collectors. (and of course they should not overwrite self.)
from http://forum.world.st/first-impressions-td4939166.html in message by Serge on Mar 19, 2017; 3:57pm