Question: The Mathura Herakles is thought to represent Herakles fighting a monster that had impervious what?

Context paragraphs:
Mathura Herakles: The Mathura Herakles is a famous statue found in the city of Mathura, India, thought to represent the Greek hero Herakles fighting the Nemean lion.

Northern Satraps: The Northern Satraps are a dynasty of Indo-Scythian rulers who held sway over the area of Mathura and Eastern Punjab from the 1st century BCE to the 2nd century CE.  They are called "Northern Satraps", in opposition to the "Western Satraps" ruling in Gujarat and Malwa at roughly the same time.  They are thought to have replaced the last of the Indo-Greek kings in the Eastern Punjab, as well as the Mitra dynasty and the Datta dynasty of local Indian rulers in Mathura.

SQRL: SQRL or Secure, Quick, Reliable Login (pronounced "squirrel" /ˈskwɝl/    ) (formerly Secure QR Login) is a draft open standard for secure website login and authentication.  The software solution typically uses a link of the scheme sqrl:// or optionally a QR code, where a user identifies via a pseudonymous zero-knowledge proof rather than providing a user ID and password.  This method is thought to be impervious to a brute force password attack or data breach.  It shifts the burden of security away from the party requesting the authentication and closer to the operating system implementation of what is possible on the hardware, as well as to the user.  SQRL was proposed by Steve Gibson of Gibson Research Corporation in October 2013 as a way to simplify the process of Authentication protocol, without requiring a third party, thus possibly revealing information about the transaction.

Nemean lion: The Nemean lion ( ; Greek: Νεμέος λέων "Neméos léōn"; Latin: "Leo Nemeaeus" ) was a vicious monster in Greek mythology that lived at Nemea.  It was eventually killed by Heracles.  It could not be killed with mortals' weapons because its golden fur was impervious to attack.  Its claws were sharper than mortals' swords and could cut through any armor.

Buddhist symbolism: Buddhist symbolism is the use of Buddhist art to represent certain aspects of dharma, which began in the fourth century BCE.  Anthropomorphic symbolism appeared from around the first century CE with the arts of Mathura and the Greco-Buddhist art of Gandhara, and were combined with the previous symbols.  Various symbolic innovations were later introduced, especially through Tibetan Buddhism.

Gomitra: Gomitra was one of the first rulers of the Mitra dynasty, a group of rulers whose name incorporated the suffix "-mitra" and who are thought to have ruled the area of Mathura from around 150 BCE to 50 BCE.  It is thought that Gomitra ruled during the second half of the 2nd century BCE.

Hagamasha: Hagamasha was an Indo-Scythian Northern Satrap (ruled in Mathura in the 1st century BCE, probably after 60 BCE).  In central India, the Indo-Scythians are thought to have conquered the area of Mathura over Indian kings around 60 BCE, thus founding the Northern Satraps.  Some of their first satraps were Hagamasha and Hagana, who were in turn followed by Rajuvula, but according to some authors, Rajuvula may have been first.

Mitra dynasty: The Mitra dynasty refers to a group of local rulers whose name incorporated the suffix "-mitra" and who are thought to have ruled the area of Mathura from around 150 BCE to 50 BCE.  They are not known to have been satraps nor kings, and they coins only bear they name without any title, therefore they are sometimes simply called "the Mitra rulers of Mathura".  Alternatively, they have been dated from 100 BCE to 20 BCE.  The Mitra dynasty was replaced by the Indo-Scythian Northern Satraps from around 60 BCE.

Kobalos: The kobalos (pl.  kobaloi) was a sprite from Greek mythology, a mischievous creature fond of tricking and frightening mortals.  The kobaloi were companions of Dionysus and could shapeshift as Dionysus in the guise of Choroimanes-Aiolomorphos.  According to one myth, they robbed Herakles while he slept.  He captured them in revenge but took pity on them when he found them amusing.  In one version of the myth, Herakles gave them to the Lydian queen Omphale as a gift.  The "kobaloi" were thought to live in Euboea or near Thermopylae.  Parents used tales of the "kobaloi" to frighten children into behaving.

Negative number: In mathematics, a negative number is a real number that is less than zero.  Negative numbers represent opposites.  If positive represents movement to the right, negative represents movement to the left.  If positive represents above sea level, then negative represents below level.  If positive represents a deposit, negative represents a withdrawal.  They are often used to represent the magnitude of a loss or deficiency.  A debt that is owed may be thought of as a negative asset, a decrease in some quantity may be thought of as a negative increase.  If a quantity may have either of two opposite senses, then one may choose to distinguish between those senses—perhaps arbitrarily—as "positive" and "negative".  In the medical context of fighting a tumor, an expansion could be thought of as a negative shrinkage.  Negative numbers are used to describe values on a scale that goes below zero, such as the Celsius and Fahrenheit scales for temperature.  The laws of arithmetic for negative numbers ensure that the common sense idea of an opposite is reflected in arithmetic.  For example, − − 3 = 3 because the opposite of an opposite is the original thing.

Supporting paragraphs: Mathura Herakles Nemean lion
Answer: fur