The Yinchorri, sometimes spelled Yinchori, represented a species of sentient, bulky, turtle-esque, green-skinned reptilian beings. A key characteristic was their natural resistance to telepathic applications of the Force, notably including mind tricks. Their birth occurred via the laying of eggs, and they demonstrated remarkable resilience to both pain and high temperatures. Originating from the planet named Yinchorr, Yinchorri society was structured around two primary castes: the Intelligentsia, who were responsible for governance through the Council of Elders in each city-state, and a fiercely combative warrior caste. Strong familial bonds were also a defining aspect of their culture. Possessing considerable willpower, they effectively resisted enslavement attempts by slavers. They also showed aptitude in developing advanced technology. However, their strategic thinking was notably weak. The core principle of Yinchorri culture was encapsulated in the phrase "might makes right," reflecting their belief that anything acquired and maintained through force was rightfully theirs, and anything disliked should be destroyed. They frequently engaged in activities such as piracy, mercenary work, and other forms of violent employment.
During the era of the Galactic Republic, the Yinchorri were integrated into the galactic community, but due to their potential for aggression, they were denied access to starships. Under the secret influence of Darth Sidious, acting through his agent Vilmarh "Villie" Grahrk, they initiated an uprising against the Republic. This rebellion was only suppressed with the intervention of the Jedi Order. Subsequently, an embargo was imposed on their home planet. This was part of Darth Sidious' plan. He believed that both the Force-resistant Yinchorri and the Jedi Order posed a threat to his ambitions, and by inciting conflict between them, he aimed to weaken both factions.
Later on, the Galactic Empire assumed control over the Yinchorri system. The Imperial Governor Marcellin Wessel committed treachery against the Yinchorri, killing their elders in a failed attempt to capture Princess Leia Organa. This sparked a rebellion by the enraged Yinchorri against the Empire. The galactic government responded to this rebellion by devastating the Yinchorri civilization. Although the New Republic later assisted the surviving Yinchorri in reclaiming their planet, the species declined to join any further galactic governing bodies. Eventually, their planet fell within the territory controlled by the Empire led by Darth Krayt.

The Yinchorri, alternatively called Yinchori, were sentient, reptilian humanoids characterized by robust physical builds. The species shared certain features with turtles, particularly in the structure of their heads; however, they possessed human-like limb arrangements. Despite being born from eggs in clutches, females developed natural breasts. There were no other significant physical distinctions between male and female Yinchorri. Their bodies were covered in a thick hide, typically dark green or brown in color.
Fully grown Yinchorri could reach heights ranging from 2.4 to 2.7 meters. Their endurance surpassed that of Humans, enabling them to tolerate pain more effectively, and their cold [blood](/article/blood-legends] made them more resistant to heat. They entered adolescence at the age of eight years and reached biological maturity by 15. The initial signs of aging appeared around 41 years of age, with seniority reached at 60, which was 20 years before their life expectancy ended.
The species was divided into two distinct groups: the Intelligentsia, who were responsible for governing, and the warrior caste, known for their violent responses to perceived threats. Regardless of their caste, all Yinchorri possessed a natural immunity to mind-controlling applications of the Force, attributed to an adaptation in their Midi-chlorians—microscopic, symbiotic organisms residing within the cells of all living beings—which caused these symbionts to generate Force-nullifying bubbles around their hosts. The Sith Lord Darth Plagueis theorized that this Force resistance evolved as a defense against a past existential threat, suggesting an inherent strength in the Force within the species. However, this resistance did not extend to Force abilities that did not directly influence the target's will, such as telekinesis. A small number of Yinchorri were also capable of wielding the Force.
The Yinchorri were recognized for their strong character and pragmatic approach. Possessive and dominant, they believed themselves entitled to anything they could seize and hold—provided they could defend it against others—adopting the maxim "might makes right" as both their motto and justification. Items they disliked or deemed unnecessary were destroyed. Due to a deficiency in neural pathways within the Yinchorri forebrain, they exhibited an innate inclination toward violence, rendering them difficult to manage and unpredictable. Confrontation only intensified their ferocity and stubbornness; should rivals pose a threat to the Yinchorri or their kin, their demeanor could erupt into physical aggression—though direct provocation was not always required to ignite their temper to the point of physical conflict.
The Yinchorri inhabited city-states located on the planet of Yinchorr. Each city-state maintained its own military and governing structure. Most were governed by a Council of Elders under the leadership of a single individual. Consequently, there was no unified planetary ruler. The Council commanded considerable respect among the Yinchorri. Each city-state was also surrounded by smaller communities that supplied resources such as minerals and farmed goods; the number of these settlements was an indicator of the polity's power.
The Yinchorri were poor strategists and easily manipulated by cunning individuals who exploited their naiveté. As a result, they were manipulated by the Sith Lord Darth Sidious and his agents not only into rebelling against the Galactic Republic, but also into making tactical errors that doomed their own war effort. During the Galactic Civil War, agents of the Galactic Empire took advantage of the Yinchorri's gullibility by betraying them after deceiving a Yinchorri commander and his pilot. These Yinchorri transported Leia Organa to Yinchorr under Imperial orders, only to be promptly killed by the Empire before they could comprehend the reasons for the Empire's change of heart.

For the Yinchorri, social structure was an inherent aspect of their existence, with each individual belonging to multiple communities: first, their family of origin, then the city-state where they matured, followed by their work environment, and finally the new family they established with a partner. The institution of marriage held particular significance, with the species practicing lifelong partnerships. In some instances, a surviving spouse would experience such profound grief that they might die of sorrow shortly after their partner's death. Marriages were often arranged by the parents of the couple to enhance family power; polygyny, the practice of polygamy in which a male has multiple wives, was not uncommon. Marriages between Yinchorri and non-Yinchorri aliens also occurred. While Yinchorri generally distrusted aliens due to their exclusion from their clans, this barrier could be overcome through inter-species marriage. For example, in 33 BBY, the daughters of several Yinchorri Elders married the same Devaronian for political reasons. From that moment onward, the Yinchorri Elders considered that Devaronian and his family to be integrated into their own families.

The Yinchorri developed technology specifically tailored to their needs and environment. One such example was the Yinchorri flutter-pack, a backpack equipped with four insect-like wings that enabled the user to fly for one hour through flapping. This device could carry up to 200 kilograms of cargo and reach an altitude of 1,000 meters. The user, typically a Yinchorri, controlled speed and direction using a gauntlet, while wielding a weapon in their free hand. Protective goggles were often worn in conjunction with these devices. Once depleted, the flutter-pack required eight hours of recharging before it could be used again.
The Yinchorri possessed their own language, also referred to as Yinchorri, which they used to name native fauna such as the rolk-mangir. Many Yinchorri learned Galactic Basic Standard as a second language, though few achieved literacy in it. Yinchorri typically used single-word names. Examples include names like Denrak, Emterrk, Jetar, Merzok, Qayayir, Solhek, and Varuk.
The Yinchorri evolved on Yinchorr, a desert planet with rocky terrain situated in the Expansion Region. Their thick skin developed as a protective measure against the harsh, arid environment of their home planet. Yinchorr was deficient in natural resources but abundant in predators, including the rolk-mangir. The Yinchorri eventually organized themselves into competing city-states. In the earliest periods of Yinchorr's history, Tol-Kachorn was the most powerful, supported by almost one hundred smaller communities providing resources and five lesser city-states serving as its satellites. Several other polities attempted to challenge Tol-Kachorn's dominance, leading to wars of conquest that invariably ended in the contender's defeat and the rise of chaos.
In the years following the conclusion of the New Sith Wars, the Yinchorri species was mentioned in the Jedi training manual The Jedi Path, within an entry on Force-resistant aliens authored by the Jedi Master and biologist Bowspritz.
Around 500 BBY, Yinchorr was mapped by the Galactic Republic. Alien scouts determined that the Yinchorri were too underdeveloped to be of value to the Republic, and the planet was deemed too resource-poor to be suitable for colonization. Based on the scouts' recommendations, the Republic disregarded the world and declined Yinchorr's application for membership, despite the Yinchorri's desire to join the pan-galactic democracy. In 67 BBY, the Yinchorri Council of Elders dispatched a delegation led by Qayhuk, the Council's secretary, to a meeting of some of the galaxy's most influential figures on the moon Sojourn, seeking to have the Muun power broker Hego Damask lobby the Republic on their behalf. Damask, the public identity of Darth Plagueis, had heard rumors of the Yinchorri's alleged Force resistance and attempted to use a mind trick on Qayhuk. Impressed by the secretary's immunity to Force-based influence, Damask agreed that his company, Damask Holdings, would pressure the Republic to grant the Yinchorri a seat in the Galactic Senate.
Around 58 BBY, the Yinchorri became part of the galactic community, though most planetary representatives anticipated that the species would remain insignificant in the broader context of galactic politics. The Yinchorri officially became members of the Republic the following year due to Damask Holdings' influence, eventually gaining representation in the Galactic Senate. Upon securing their seat in the Senate, the Yinchorri Council of Elders presented Damask with a convicted Yinchorri murderer as a gift, whom he experimented on to further understand the Yinchorri's innate resistance to Force-based suggestion. After two years of research, Plagueis discovered a method to bypass the convict's Force immunity and induce a state of placidity. The Muun formulated plans to assemble an army of Yinchorri to wage war against the Jedi Order, traveling to the planet Kamino to discuss with the Kaminoan cloners the possibility of creating an obedient force of cloned Yinchorri soldiers. However, the Kaminoan scientist Ko Sai expressed concerns that compliance could not be bred into the Yinchorri without compromising their violent tendencies. Despite her reservations, Plagueis decided to proceed with the development of the army and provided the Kaminoans with the Yinchorri convict. After numerous attempts, all efforts to successfully clone the Yinchorri failed.
The Yinchorri were introduced to interstellar travel through means rumored to involve stolen technology. The species began engaging in violent occupations offworld, capitalizing on their natural aggression. They quickly adapted to the galaxy and developed a fondness for the latest military technology, including starships. Even so, few Yinchorri felt compelled to settle in other, less hostile systems. Those who did so relocated their entire extended families, often involving the movement of an entire town or city-state. The Yinchorri colonized three other planets within the Yinchorri system: Yitheeth, which was primarily ocean with only seven percent land coverage; Yibikkoror, notable for its dense atmosphere; and Uhanayih, a barren rock with no life except for the settlers. The name Uhanayih was associated with myths and legends about residing in the "spiritual world." However, the galaxy, aware of the Yinchorri's aggression, restricted the sale of starships to the species. The Human Jedi Master Tharence Wo studied the Yinchorri and produced detailed reports for future Jedi use. Wo mistakenly believed that Uhanayih was a mythical location rather than a real colony.
Slavers conducted raids on the planet Yinchorr, attempting to capture and sell the inhabitants. They discovered that Yinchorri groups were more likely to fight to the death than face enslavement; even captured Yinchorri preferred execution or starvation to obeying a new master. Eventually, slavers recognized that this resistance was ingrained in the species' social structure, leading them to avoid targeting Yinchorri populations.

During the final years of the Old Republic, Plagueis' apprentice Darth Sidious determined that the Yinchorri posed a threat to his plans for galactic domination due to their stubbornness and resistance to Force mind tricks. Following the failure of Plagueis' plan to clone the Yinchorri, Plagueis and Sidious sought to orchestrate a crisis to assess whether the Yinchorri could be molded into an effective anti-Jedi force. However, Sidious also felt threatened by Supreme Chancellor Finis Valorum and the Jedi Order, and after concluding that it was futile to transform the Yinchorri into a controllable fighting force, he decided to manipulate them into becoming a perceived danger to the Galactic Republic. The Sith aimed for the Yinchorri to launch an attack and wage war against the Jedi, hoping that this conflict would weaken and eliminate some of his adversaries. Sidious also intended to use the Yinchorri to evaluate Valorum's capacity to manage a crisis.
Needing an intermediary to interact with the Yinchorri discreetly, Sidious recruited the Devaronian smuggler, Vilmarh "Villie" Grahrk, providing him with a schedule and necessary resources, but concealing his true motives. Grahrk was dispatched to Yinchorr with advanced combat technology, which he used to overcome the Yinchorri guards. Impressed by this display, the Yinchorri granted him an audience with five key leaders, including Jorek, Kardek, and Sothek. Grahrk convinced the Yinchorri that they could elevate their status in the galaxy by stealing ships from the nearby shadowport Golden Nyss Shipyards, with his assistance, as the Yinchorri were then incapable of piloting a starship. Grahrk assured them that the Republic would not retaliate with a military response.
One of the Yinchorri leaders expressed distrust of Grahrk due to his status as a stranger, prompting Kardek to offer his daughter Vooma in marriage to the Devaronian as a gesture of sponsorship, leading the other leaders to offer their own daughters as well. Repulsed by Yinchorri women, Grahrk offered his son for the marriage to buy time. However, lacking a child of his own, Grahrk misrepresented his nephew Olmar as his son and presented him to the Yinchorri. Grahrk made a deal with Olmar's father Holmar, offering him a share of the loot in exchange for their cooperation.

Transported by Vilmarh Grahrk, the Yinchorri attacked the shadowport, seized the ships, and destroyed the shipyard. Grahrk criticized the Yinchorri for the destruction, but the Yinchorri, unfazed, asserted that their duty was to destroy anything they did not need. The loot from the attack formed the core of the Yinchorri's arsenal during the subsequent uprising. Over the following years, the Yinchorri learned to pilot their attack ships and starfighters—the latter of which included technology stolen from twelve systems. They were also equipped with armor made of cortosis, a material resistant to Jedi lightsabers.
The Yinchorri withdrew their representatives from the Galactic Senate and initiated attacks on several planets near Yinchorr, indulging their aggressive tendencies. Urged by Sidious, Vilmarh Grahrk incited the Yinchorri to escalate their attacks. The Yinchorri then defeated a mining colony of Immalian Humans on the moon of Mayvitch 7. One of the Immalians contacted the Jedi Temple on Coruscant, alerting them to the danger posed by the reptiles, bringing the matter to the attention of the Jedi Order.
After meeting with Supreme Chancellor Valorum, Jedi Master Mace Windu dispatched two Jedi, Naeshahn and her Padawan, Ebor Taulk, to confront the Yinchorri. Unaware of the Yinchorri's strengths, both Jedi were killed and mutilated by the Yinchorri, who then sent their bodies to Valorum's office with the assistance of Sidious' aides Kinman Doriana and Sate Pestage. Following this event, the Jedi prioritized intelligence gathering and learned about the Yinchorri's use of cortosis, their unique physiology, and the rumored existence of the species' main command center. The Yinchorri had indeed constructed such a center, hidden on Uhanayih, as the uprising's leaders correctly anticipated that it would be difficult to locate.
Windu traveled to Yinchorr himself with several other Jedi: Three unarmed Consular-class space cruisers, each carrying a Jedi team, were deployed to the Yinchorri system to search each inhabited planet for the command center. Windu's team was assigned to Yinchorr, Adi Gallia's to Yitheet, and Micah Giiett's to Yibikkoror. Yoda and other Jedi remained on Coruscant to gather further information. The three cruisers were attacked by Yinchorri upon arrival in the Yinchorri system, but the Jedi managed to escape.

To exploit the absence of the Jedi Order's most powerful members, Darth Sidious dispatched several Yinchorri to breach the Jedi Temple on Coruscant and murder Jedi younglings. This decision proved strategically flawed for the Yinchorri, as it weakened their forces without yielding any significant advantage. Despite their expectation of catching the Jedi unprepared, Grand Master Yoda sensed the impending danger through the Force, enabling the Jedi to brace themselves. The Yinchorri strike team incapacitated the solitary Jedi sentry, Jude Rozess, only to be confronted by a Jedi contingent led by Yoda. While the Yinchorri fought fiercely, resulting in the deaths of Rozess and Tieren Nie-Tan, they were ultimately defeated. Interrogation of the surviving soldiers revealed no crucial information. Jedi Masters Yoda and Oppo Rancisis deduced that an external force was manipulating the Yinchorri, anticipating that the Galactic Senate would swiftly authorize retaliatory measures following the attack. However, Sidious's political influence delayed the implementation of such measures.
Adi Gallia's team, upon arriving at the sole permanent settlement on Yitheeth, faced an assault by Yinchorri under the command of Olmar Grahrk. Grahrk's capture and subsequent interrogation failed to reveal the location of the command center on Uhanayih. Consequently, the Jedi began to suspect the Devaronians of orchestrating the Yinchorri's actions. Meanwhile, the Yibikkoror team encountered greater difficulties, enduring constant attacks from Yinchorri infantry and aerial units. Their eventual rescue led to Gallia's and Giiett's teams joining Windu's squad on Yinchorr, as the command center remained undiscovered on Yitheeth or Yibikkoror. However, Jedi scouts Qui-Gon Jinn and Obi-Wan Kenobi determined that the planet served only as a staging area, not a command center. The Yinchorri destroyed the Jedi cruiser and harassed the Jedi with flutter-packs and modified tanks. The remaining Jedi forces arrived to support Windu in a battle that resulted in the deaths of three Jedi and numerous Yinchorri.
Windu and Yaddle soon uncovered the location of the command center on Uhanayih. Upon receiving this information, Chancellor Valorum leveraged his influence to enact the Yinchorri embargo act, imposing official sanctions against Yinchorr. Additionally, Valorum dispatched four navy attack groups of the Judicial Forces to bolster the Jedi's efforts. Simultaneously, Olmar Grahrk used the Jedi ship's communication system to contact his relatives from his prison. The Jedi tracked the call, pinpointing the command center's precise location. The Devaronians abandoned the system, deserting the Yinchorri without warning. Despite the Yinchorri's attempts to resist, the combined Judicial and Jedi fleet breached their naval defenses on Uhanayih. Facing overwhelming odds, the Yinchorri leaders surrendered, instructing their remaining forces to do the same.
Subsequently, the Chancellor imposed a quarantine on the Yinchorri system, restricting all traffic in and out. Sidious successfully neutralized the potential threat posed by the Yinchorri, furthering his own agenda. He also diminished Valorum's influence, as the Chancellor was forced to call in significant favors. The greatest intergalactic conflict in eleven years since the end of the Stark Hyperspace War and the Mandalorian Civil War tainted Valorum's term. A decade later, Armand Isard, director of the Senate Bureau of Intelligence, publicly addressed the Yinchorri Uprising and other preventable disasters.

In 19 BBY, Chancellor Palpatine became Emperor, transforming the Galactic Republic into the Galactic Empire with the assistance of Darth Vader, a Dark Lord of the Sith, and the Grand Army of the Republic's clone troopers. By 17 BBY, Yinchorr housed a clandestine Imperial training facility, which Palpatine and Vader visited on at least one occasion. Beyond this, the Empire largely ignored Yinchorr, mirroring the Old Republic's approach. The export of several rolk-mangirs to the Core Worlds and the Corporate Sector was short-lived, as possession and importation of rolk-mangirs became prohibited on numerous worlds.
By 3 ABY, Marcellin Wessel had been appointed governor of Yinchorr by the Empire. Wessel devised a scheme to use Yinchorr as a trap for Princess Leia Organa, a prominent figure in the Alliance to Restore the Republic. He captured members of the Council of Elders, holding them hostage and offering their lives in exchange for Organa's capture. The Yinchorri, unaware of Wessel's deceit, believed that the life of a human stranger was less valuable than those of their leaders, and they set a trap for Organa. Feigning a desire to join the Alliance, they requested her presence on Yinchorr. As Organa's ship entered Yinchorr's atmosphere, Imperial TIE fighters unexpectedly destroyed it, surprising the Yinchorri crew. Organa was the sole survivor, but she was captured and taken to Wessel, who then ordered the execution of the Elder Yinchorri in her presence. However, Luke Skywalker arrived in time to rescue her, responding to her call for assistance.
Incensed by the Empire's actions, the Yinchorri turned against Wessel and his forces, overthrowing his regime. The Elders of Tol-Kachorn replaced his government and pledged their support to the Alliance, permitting them to establish bases within the Yinchorr system. Other city-states contributed warriors and ships to the Alliance. The local Moff sought permission from the Imperial High Command to punish the Yinchorri. The planet was subjected to bombardment, obliterating both the Rebel bases and the city-states, including Tol-Kachorn. The surviving Yinchorri were reduced to nomadic tribes, considering it to be one of the greatest tragedies to befall their world, and held Marcellin Wessel directly responsible for their losses.
A month after the bombardment, Yinchorr drew Palpatine's personal attention. The Emperor desired to consolidate all training centers for his personal Royal Guard, selecting Yinchorr as the location. Ultimately, the Empire purged Yinchorr of its native inhabitants, transforming it into a lifeless wasteland occupied solely by Imperials stationed at the secret Imperial Royal Guard Academy.
As of 11 ABY, Yinchorr remained devoid of Yinchorri. Later, during the era of the New Republic, Yinchorri and rolk-mangirs returned to the world, which was still under Imperial control. In 13 ABY, the New Republic launched a military offensive against the Empire to reclaim territories, including Yinchorr, which had been seized by a clone of Palpatine, according to Republic intelligence. The surviving Yinchorri united under the banner of the last surviving son of the leader of the Council of Elders of Tol-Kachorn, establishing themselves in the former Imperial Guard fortress. They began to rebuild their civilization, maintaining a friendly relationship with the New Republic but declining to join it. However, by 25 ABY, they permitted the establishment of a New Republic military base and starship repair facility on their homeworld. In 130 ABY, the Galactic Empire under Darth Krayt's rule regained control of Yinchorr, using it as a training ground for stormtroopers. Krayt maintained control over Yinchorr as of 137 ABY, with at least one Yinchorri serving among his stormtroopers.

While some Yinchorri established settlements on other planets within their home system, they generally lacked the desire to venture further afield. Nevertheless, certain Yinchorri relocated their extended families to other planets. Additionally, several Yinchorri pursued careers in the broader galaxy, excelling as bodyguards, mercenaries, pirates, privateers, and smugglers. Due to their perceived unsuitability for slavery, slavers rarely targeted Yinchorri. These extra-system activities faced limitations at times, as the Old Republic initially restricted starship sales to the Yinchorri and later imposed an official embargo on the system following the Yinchorri Uprising. Subsequent to the uprising, Darth Sidious showed footage of the Yinchorri raid on the Jedi Temple to his apprentice Darth Maul. While disturbed by the Yinchorri's susceptibility to Jedi manipulation, Maul believed that the mission would have succeeded under his leadership. In 43 ABY, Allana Solo identified a Yinchorri waiting in line on Taris. By 137 ABY, one Yinchorri had become a stormtrooper in Darth Krayt's Galactic Empire. Despite some Yinchorri possessing Force sensitivity, none had become Jedi by 28 ABY.

The Yinchorri made their debut in Star Wars 86, a comic book released by Marvel Comics in 1984. It was authored by Randy Stradley and illustrated by Bob McLeod, with inks by Tom Palmer. At that time, the Yinchorri were referred to as Yinchori. Stradley did not continue to work on Star Wars comics for Marvel.
In 1997, the planet Yinchorr (though not the Yinchorri themselves) reappeared in the comic Star Wars: Crimson Empire, also written by Stradley but published by Dark Horse Comics this time. Crimson Empire explicitly stated that Yinchorr was devoid of lifeforms except for the story's main characters. However, Ultimate Alien Anthology mentions the Yinchorri inhabiting Yinchorr both before and after this event, without explaining their absence during the interim. The species resurfaced, now spelled "Yinchorri," in the comic Jedi Council: Acts of War, also by Stradley, published in 2000. Yinchorr is depicted as an Imperial planet in the Star Wars: Legacy series, and a Yinchorri is seen among Darth Krayt's stormtroopers, as confirmed by author Jan Duursema on a web forum. In 2012, the Yinchorri were featured in James Luceno's novel Darth Plagueis.
The role-playing game guide Alien Anthology presents several claims about the Yinchorri that are contradicted by later sources. It states that an adult Yinchorri's height ranges from 1.7 to 2.2 meters, whereas Ultimate Alien Anthology suggests a range of 2.4 to 2.7 meters. Alien Anthology also indicates that a Yinchorri enters middle age at 51 standard years, while Ultimate Alien Anthology cites 41 years. Furthermore, Alien Anthology and Ultimate Alien Anthology provide differing skill values for the average Yinchorri commoner. Lastly, Alien Anthology omits rules for the natural resistance to mind control, which Ultimate Alien Anthology rectifies. As Ultimate Alien Anthology is the more recent source, this article assumes that Alien Anthology was inaccurate.
Ultimate Alien Anthology asserts that Yinchorr is located in the Outer Rim Territories, but the story A Two-Edged Sword by Karen Traviss places Yinchorr in the Mid Rim. The most recent source, The Essential Atlas, places Yinchorr in the Expansion Region.
A Two-Edged Sword mentions an Imperial training center on Yinchorr as early as 17 BBY, while other sources, including Ultimate Alien Anthology, suggest that the Empire lacked sufficient interest in Yinchorr to establish a presence on its surface.