00452naa#a2200169#i#450# EN\INFRA-M\bibl\14083 20240425193915.4 2308-4898 20161219b2016####ek#y0engy0150####ca RUS RU Envelope of a Family of Curves Journal article Moscow INFRA-M Academic Publishing LLC. 2016 4 с. Journal article local Girsh A. G. riorpub.com