2552



2552 was the penultimate year in the Human-Covenant War. During which, the Humans of the United Nations Space Command nearly saw utter defeat and extinction, though the tide turned, and with the help of the Sangheili, won the war. The Covenant were at the peak of their power and reach in 2552, with major assaults on the Human Inner Colonies and two large invasions of their homeworld, Earth. During the battle at Installation 04, the galaxy found it's first large outbreak of the Flood threat in over a hundred thousand years. Over two months later, an even larger outbreak occurred at Installation 05.

The war finally drew to a close at Installation 00, known more commonly as the "Ark", with the Humans and Sangheili attempting to assassinate the High Prophet of Truth, before he could activate the remaining Halo Installations. The alliance was successful in their mission against the Covenant, which was later presumed to be disbanded.

July
July 17th
 * The Slipspace probes from the Archimedes encounter the Covenant ships sent to attack Sigma Octanus IV
 * The is tasked with patrolling the Sigma Octanus Star System
 * The Battle of Sigma Octanus IV begins.

July 18th
 * The UNSC win a victory during the battle at Sigma Octanus IV. Commander Jacob Keyes, of the, plays a critical role in this success. Keyes is subsequently promoted to Captain by Admiral Stanforth. Unknown to the UNSC, the Covenant place a tracker on the hull of the Iroquois. The importance of Reach to the UNSC is revealed to the Covenant when the Iroquois returns to that world.

August
Early August
 * The crashes in lunar orbit, knocking out communications within the Solar System for seven seconds.

August 12th
 * SPARTAN-117 and Corporal Harland are debriefed by ONI at Camp Hathcock, Reach, on the events on Cote D'Azur during the Battle of Sigma Octanus IV.

August 25th
 * Dr. Halsey and Cortana choose the, with Jacob Keyes as her commander, for a secret mission Halsey is planning.

August 27th
 * All but three SPARTAN-IIs gather at the FLEETCOM Military Complex on Reach, where they learn of their next mission: to acquire a Covenant vessel, navigate to the Covenant home world, and return with captured Covenant leadership.

August 29th
 * SPARTAN-117 receives a neural interface upgrade, armor, and is introduced to Cortana.

August 30th
 * Cortana has ONI Colonel James Ackerson illicitly transferred to the front. This is her revenge for his attempts to eliminate both her and SPARTAN-117.
 * First Lieutenant Jake Chapman, along with most of Charlie Company is killed at The Battle of Reach.
 * The Covenant, despite sustaining heavy losses, win a crushing victory at the Battle of Reach. Many of the remaining SPARTAN-IIs are killed.
 * The escapes the disaster at Reach although, due to Cortana, the jump is not blind as per the Cole Protocol dictates.
 * The surviving SPARTAN-IIs on Reach are separated into two groups. One recovers Vice Admiral Whitcomb and goes into hiding at Camp Independence. The others are admitted into CASTLE Base by Dr. Halsey and receive parts of the MJOLNIR Mark V upgrade and new weapons.
 * Dr. Halsey learns of Colonel Ackerson's mysterious plans that seem to involve "her" Spartans.

September

 * Coral is reported glassed by the Covenant.

September 4th
 * Lieutenant Wagner returns to Earth and reports on the evident destruction of Reach to Colonel James Ackerson, Admiral Hood, and General Strauss at an ONI facility in Sydney, Australia.

September 19th
 * The arrives at Alpha Halo
 * The Battle of Installation 04 begins.
 * SPARTAN-117 is awoken from cryosleep and tasked with preventing Cortana's capture by the Covenant.
 * SPARTAN-117 and Cortana escaped the ship aboard a Bumblebee-class Lifepod, which later crashed on the ring.
 * The is forced to crash land on the ring. A significant portion of her crew survives to continue the fight on the ground.


 * Captain Keyes and the others in his escape pod are captured by the Covenant. Only Keyes escapes summary execution, and is taken to the Truth and Reconciliation.

September 20th
 * SPARTAN-117 leads a Marine force to board the Truth and Reconciliation. They recover Keyes and escape aboard a Covenant dropship. Keyes orders SPARTAN-117 to find the "Silent Cartographer", a map room that will reveal the location of the Control Room. Keyes leaves to lead an assault on a Covenant weapons cache.
 * Having found the map room and the pertinent information, Cortana directs a Pelican to take them to the area where the ring's Control Room is. Upon reaching the Control Room, Cortana transfers to the Control Room's computer and directs SPARTAN-117 to stop Keyes from accessing the 'weapons cache', really a Forerunner research and quarantine facility.
 * SPARTAN-117, without Cortana, enters the facility but is unable to locate Keyes. Instead, he discovers the "Flood" and is forced to retreat. He links up with marines and takes command of the surviving members of Keyes' team and together they fight their way to the extraction point. However, the Spartan is conscripted by the "Monitor of Installation 04" and teleported away before he can be evacuated with the surviving members.

September 21st, 2552
 * The Monitor takes SPARTAN-117 to the ring's "Library" to retrieve the "Index", a device needed to activate the ring's primary weapon. Having retrieved the Index, the Monitor teleports the Spartan back to the Control Room where an irate Cortana confiscates the Index and prevents the ring from firing. SPARTAN-117 and Cortana flee a now-hostile 343 Guilty Spark and Sentinels.
 * To forestall the ring from being activated manually, SPARTAN-117 disables the ring's three Pulse Generators. This is to buy time to destroy the ring by activating the auto-destruct on the Pillar of Autumn. Only Keyes neural interface can activate the ship's self-destruct, and SPARTAN-117 embarks once more to rescue the captain.
 * Cortana teleports the Spartan to the Flood-overrun Covenant cruiser where Keyes is being held. Alas, the pair arrives too late to save Keyes, who has been merged into a Brain Form. SPARTAN-117 retrieves the neural interface by punching in the former-captain's head. Cortana downloads the necessary codes, and the duo returns to the Pillar of Autumn on a captured Banshee.

September 22nd
 * SPARTAN-117 and Cortana rendezvous with Johnson's group in Installation 04's debris field. They also recover a set of cryotubes, one which contains SPARTAN-058.
 * 343 Guilty Spark overrides the auto-destruct codes, forcing SPARTAN-117 to manually destabilize the ship's still-functioning fusion cores. SPARTAN-117 and Cortana then escape the resulting explosion and the fragmentation of the ring aboard a Longsword.
 * Staff Sergeant Johnson, Lieutenant Haverson, Warrant Officer Polaski, Corporal Locklear also escape the destruction of the ring aboard a Pelican.
 * The Battle of Installation 04 ends. Gunnery Sergeant Stacker survives, but it is unknown how he does.

September 23th
 * As the Longsword and Pelican are not jump capable, the UNSC survivors assault and capture the Ascendant Justice, a Covenant warship and apparently the flagship of the Covenant Fleet sent to Installation 04. They then set course for Reach.
 * A Time/Date Record Anomaly continues from this point in the narrative, resolved above on Sep 7, 2552.

September's Anomaly
After the recovery of a Forerunner device on Reach, the members of an organized resistance comprised of SPARTANs from Reach and survivors of the Battle of Installation 04 are in some sort of time anomaly, causing them not to be in the "correct timeline". What is known is that the events taken place with the possession of the device take place after September 24th.

September 7th
 * The Time/Date Record Anomaly of Sept 23, 2552 most likely rejoins the correct timeline.
 * Dr. Halsey and members of Red Team discover an enigmatic shard in a Forerunner installation below CASTLE Base. They are besieged by Covenant forces who seek to possess the shard.
 * The remaining Spartans, Admiral Whitcomb, Dr. Halsey, Sgt. Johnson, Lieutenant Haverson, Warrant Officer Polaski, and Corporal Locklear jump to Slipspace on board the Covenant/Human hybrid ship Gettysburg-Ascendant Justice, and discover that the shard seems to have the ability to bend both space and time.

September 12th
 * The Gettysburg/Ascendant Justice arrives for refit and provisioning in Eridanus system and meets with the rebels under Governor Jiles. Dr. Halsey sedates Spartan 087, Kelly, and absconds with her on Governor Jiles' personal ship, the Beatrice. Before she goes, she gives the alien artifact to Corporal Locklear, with implicit instructions to destroy it.

September 13th
 * UNSC forces aboard the Gettysburg/Ascendant Justice win a crucial victory at the Battle of the Unyielding Hierophant. SPARTAN-093, Lieutenant Haverson of ONI and Vice Admiral Whitcomb are killed. The survivors, now aboard the singular and with a captured Covenant slipspace drive, depart for Earth to warn of the impending Covenant invasion.

October
October 20th
 * SPARTAN-117 is outfitted with the MJOLNIR Mk. VI aboard Cairo Station.
 * The Fleet Commander of Particular Justice is deemed a Heretic by the Covenant High Council and sentenced to death.
 * SPARTAN-117 and Staff Sergeant (now promoted to Sergeant Major) Johnson are decorated at a ceremony aboard Cairo Station. Captain Keyes is awarded posthumously and the decoration is entrusted to Commander Keyes.
 * The First Battle of Earth begins.
 * The High Prophet of Regret's fleet arrives at Earth, not expecting any human presence. The vastly outnumbered Covenant force attacks without seeking support from other Covenant forces.
 * SPARTAN-117 foils a Covenant attempt to demolish Cairo Station and commandeers the Covenant bomb to destroy an assault carrier.
 * The High Prophet of Regret's assault carrier breaks through the orbital defenses and initiates a ground assault on New Mombasa and the surrounding area.
 * SPARTAN-117 deploys to New Mombasa in an attempt to capture the High Prophet of Regret. Before this can happen, the assault carrier initiates a slipspace jump within the city, escaping Earth and destroying the city in the process.  The, with SPARTAN-117 aboard, successfully pursues the carrier through slipspace.
 * The First Battle of Earth ends.
 * The former Fleet Commander of Particular Justice is made the Arbiter by the High Prophets of Truth and Mercy.
 * The Arbiter destroys a heretic group and 'recovers' the Oracle.

October 31st
 * The Battle of Onyx begins.
 * The standby signal rouse the Sentinels of Onyx, who destroy the UNSC base on the world.
 * Kurt, Mendez, and some Spartans battle to survive the Sentinel's onslaught.

Unknown Date
 * An Edict from the Office of the High Prophet of Truth orders that all personnel were to spend today's second rest period in attentive watchfulness before display monitors. All display monitors displayed the humbling and punishment of the Sangheili Supreme Commander of the Fleet of Particular Justice, for failure, cowardice, and lack of faith.

November
November 2nd
 * The Battle of Installation 05 begins.
 * The UNSC In Amber Clad arrives at Delta Halo, following the High Prophet of Regrets assault carrier. SPARTAN-117, aided by ODSTs and marines, pursue the High Prophet to a Forerunner temple and assassinate him.  However, orbital bombardment from the escorting fleets of the newly arrived High Charity destroys the temple.  SPARTAN-117 is thrown into a lake and captured by Gravemind.

November 3rd
 * The UNSC Dusk arrives at Delta Halo and witnesses the final stages of the Battle of Installation 05. She retreats to Earth via a Slipspace Wake caused by the Forerunner ship.
 * The Dusk arrives at Earth after mere hours. Upon arrival, she is re-assigned to Battlegroup Stalingrad. The group jump to Onyx via the captured Covenant Ships Slipspace wake.
 * Battlegroup Stalingrad arrives at Onyx to retrieve the survivors, but is unsuccessful due to the Covenant presence. The UNSC battlegroup is destroyed.
 * Halsey and the other survivors hold off pursuing Covenant troops long enough to flee to the safety of the Shield World and seal the entrance.
 * Having received Halsey's signal, SPARTAN-043, SPARTAN-058, and SPARTAN-104 redeploy from Earth to Onyx aboard a captured Covenant ship. They rendezvous with Halsey. The UNSC survivors are forced to retreat underground as a newly arrived Covenant fleet beings landing troops.
 * Sentinels annihilate the remaining Covenant forces as Onyx 'disintegrates'.
 * Dr. Halsey and SPARTAN-087 arrive and are trapped along with the rest of the human survivors. Halsey sends a distress signal piggybacked on Cortana's October 28 signal.
 * Kurt dies after destroying Onyx by detonation of 2 FENRIS warheads.
 * The Battle of Onyx ends.

November 3rd through November 7th
 * The Arbiter is sent to Delta Halo to retrieve that installation's Index. The Arbiter is successful, but is then betrayed by Tarturus, who casts the Arbiter into the depths of the ringworld.  The Arbiter is subsequently captured by Gravemind.
 * The Civil War of the Covenant begins.
 * Gravemind sends SPARTAN-117 and the Arbiter to secure the Index and prevent the installation from being activated. SPARTAN-117 is teleported to High Charity while the Arbiter is teleported close to the Control Room.  Both are aided by the chaos of the Covenant civil war.
 * SPARTAN-117 is unable to prevent the Index from leaving High Charity with Tartarus. Instead, on the advice of Cortana, the Spartan stows away aboard the Forerunner ship that is carrying the High Prophet of Truth to Earth.  Cortana remains behind to ensure the destruction of Installation 05, should that become necessary.
 * Cortana sends a slipspace message to Earth informing them that SPARTAN-117 is en route.
 * The Arbiter reaches the Control Room but is unable to prevent Tartarus from activating the ring. With the help of humans and the Elites, the Arbiter kills Tarturus.  This allows Commander Keyes to physically remove the Index from the Core, temporarily interrupting the firing sequence.
 * Due to the interruption, Installation 05 automatically sends a signal to all other Forerunner installations in the galaxy, activating and placing them in standby mode.

November 8th
 * The Forerunner Dreadnought arrives in the Sol System, and proceeds on course towards Earth at near-relativistic speeds

November 17th
 * The Forerunner Dreadnought enters Earth's atmosphere, and Spartan 117 bails out, landing in the Kenyan jungles.

Unknown Date
 * An Edict from the Office of the High Prophet of Truth orders that in the virtue of the Jiralhanae, all Sangheili posted with the Fleet of Profound Solitude, the Fleet of Tranquil Composure, and the Fleet of Inner Knowledge to be completely replaced by Jiralhanae. Each removed Sangheili to be assigned other duties. In celebration, all imprisoned or criminal Jiralhanae were released, rehabilitated, and pardoned.

Fall and Winter 2552
The end of 2552 saw the bloodiest period of the Great War and the beginning of the end. The Prophet of Truth was killed in the later months along with a sizable covenant armada, leaving the Covenant forces crippled and leaderless as well as the full destruction of Gravemind and its Flood forces.

It's possible that some of these events take place in 2553.

Second Battle of Earth
 * At the beginning of the battle, Covenant Loyalist forces assaulted the Human city of Cleveland, Ohio in the United States on Earth. The Loyalists were looking for the Key of Osanalan, a mysterious Forerunner device related to the Halo Installations.
 * Later during the Second Battle of Earth, a battle at Pawas in Afghanistan took place. There, UNSC Marine Corps forces battled Loyalist forces for control of a Satellite installation. Numerous Marines of the 2nd ODST Battalion targeted the Forerunner Dreadnought entering Earth's atmosphere. Onboard was one of the last SPARTAN-II soldiers, Master Chief Petty Officer John-117.

Battle for Kenya
 * During the Battle for Earth, the Crow's Nest was an Underground Facility used by the UNSC Defense Force to coordinate local Army, Navy, and Marine forces.

Battle of Voi
 * The Prophet of Truth's fleet of twenty-odd s and two Assault Carriers led by Truth in the Forerunner Dreadnought had committed all their forces to Africa, specifically Voi, Kenya and the surrounding regions.
 * SPARTAN-117 led a UNSC counterattack to regain lost UNSC ground, retaking a jungle near Mount Kilimanjaro and securing the area around the Crow's Nest. Commander Miranda Keyes and Sergeant Major Avery J. Johnson then organized a small UNSC strike force led by SPARTAN-117 to attack the Covenant Loyalist-held Tsavo Highway, and thus have a platform for a strike at Voi.
 * The UNSC Marine Corps was able to retake the Tsavo Highway, and it served for a staging ground for the battalion that would retake Voi. The UNSC forces stationed already at Voi had already suffered severe casualties, with only pockets of Marines drawn in a scattered last defense against numerically superior and vehicle-supported Loyalist forces.
 * Fleet Admiral Sir Terrence Hood declared that it was imperative that SPARTAN-117's attack force retake Voi. Lord Hood's plan was that he would launch a low-level aerial strike on Truth's fleet above the Forerunner artifact, and prevent him from activating the presumed Ark. However, a Loyalist anti-aircraft emplacement stationed at Voi prevented Hood fleet from advancing; SPARTAN-117 was to retake Voi and destroy the anti-aircraft emplacement to allow Hood to attack Truth's fleet, and prevent him from activating the Ark.
 * They later defeated the AA guns, opening up a pocket in the Loyalist Defenses for the Home Fleet to come in and engage Truth's forces. They were successful in damaging the Dreadnought, though it was allowed to escape through the Portal, finally ending the second battle of Earth. They thought they were finished with the Battle, but there was yet one more threat they had to deal with, who was also a threat to the Covenant.
 * Commander Miranda Keyes ordered her troops to fight to the core of the Flood Battlecruiser and overload its reactors, destroying the ship and the town and any Flood along with it. The Fleet of Retribution, had followed the Flood infected ship from their blockade at Installation 05 to its arrival at Earth. They began to drop forces to push towards the ship, seeking something that lay within it. It wasn't until they came back into Traxus Facility that the Sangheili told the UNSC that Cortana, the AI formally attached to the Spartan-IIs, the, and companion of John-117, was supposedly upon the downed ship.
 * The joint UNSC/Separatist force pressed on, still giving their all to getting to the crash site. They eventually broke through, fighting past Flood Pure Forms. With the remaining forces giving cover to the Chief, he entered its Floodformed carcass and retrieved what was believed to be Cortana. After the ground forces were evacuated safely the Elites began to glass the immediate area, annihilating the Flood and eliminating any chance of further Flood infection, effectively ending the Battle of Voi.

Battle of Installation 00
 * The Prophet of Truth, having successfully activated the artifact in Kenya, left Earth through a Slipspace portal to the Ark, a Forerunner structure that could be used to fire all of the Halo installations at once.
 * Despite Lord Hood's urging, Commander Keyes took ships from the Home Fleet with a small fleet of Separatist cruisers led by the carrier Shadow of Intent and proceeded through the Slipspace portal and arrived at the Ark.
 * The Separatists on arrival immediately engaged the Loyalist fleet stationed to protect the Prophet while the Forward Unto Dawn deployed Marine Shock Troopers to locate Truth. Despite being outnumbered 3-to-1 in space, the Separatist fleet made short work of the Loyalist space forces, likely due to the Elites' superior tactical skills. The Covenant Loyalist Fleet had been destroyed and the only Loyalists left alive were Truth and his forces on the Ark. 343 Guilty Spark, now working with the UNSC-Separatist Alliance, led SPARTAN-117 and the Arbiter to the Ark's Cartographer where they pinpointed the Prophet's location. By then Truth had already holed himself in a secure facility near the core of the Ark and had activated a large barrier around the entire core to ward off the attacking forces.
 * The UNSC ground forces, along with Separatist reinforcements, assaulted three emitter pylons that powered a small section of the barrier. When the defending forces were eliminated and the pylons shut down, the Shadow of Intent began its attack on Truth. At the same time the former Covenant city ship High Charity arrived from slipspace and crashed on the Ark. Debris, spread from the city-ship, heavily damaged the Shadow of Intent and helped spread a new Flood infestation on the Ark as a means to stop Truth and to be safe from the Halo activation array. Without any heavy support, SPARTAN-117 and the Arbiter personally attacked the facility where Truth was to activate the Halo installations.
 * Sergeant Major Johnson, who had disappeared during the assault on the towers, was in fact captured by Truth's forces and was being tortured into pressing the final switch to activate the other Halos, as fail-safes within the structure prevented anyone other than a Forerunner or a Reclaimer to do so. With SPARTAN-117 and the Arbiter too far away to stop Truth, Commander Keyes grabbed a Pelican dropship and crashed into the facility to rescue Johnson, but was killed soon thereafter by Truth himself. The Gravemind dispatched Flood forces to assist SPARTAN-117 and the Arbiter in order to prevent the activation of the Halo Array system; their support enabled the Master Chief and the Arbiter to reach Truth in time. The Arbiter personally killed Truth with his sword. However, the Gravemind betrayed the two of them after knocking them out of Keyes' Pelican,(then piloted by Johnson and also carrying the Commander's body), thwarting their plan of escape and forcing SPARTAN-117 and the Arbiter to fight their way outside.

Raid on High Charity
 * 343 Guilty Spark had managed to facilitate the making of a new Halo through the Ark, explaining that a tactical pulse from it would eliminate the Flood infestation. However, this new Halo lacked an Activation Index. The only way they could get another Index was to rescue Cortana from High Charity since she still possessed the Index from Installation 04. Through a tough battle, SPARTAN-117 and the Arbiter successfully entered the ruins of High Charity and recovered Cortana, using a partly-damaged Pelican to escape while High Charity was destroyed when its reactors went critical after the Spartan blasted them.

End of Human-Covenant War
 * With the Index secure, the Arbiter ordered that the remaining UNSC forces relocate to the Separatist ships and escape back through the Slipspace portal to Earth while he, SPARTAN-117 and Sergeant Major Johnson moved in on the Control Room of the incomplete Halo, the latter coming in alone aboard the Forward Unto Dawn. The Dawn was left behind as the only means of escape. By now what was left of the Gravemind had relocated to the new Halo. The Arbiter, Johnson, and SPARTAN-117, along with with 343 Guilty Spark made it through waves of Flood to the Control Room. 343 Guilty Spark explained that the new Halo would be ready to fire within days, but with Flood moving in all around them Johnson explained the necessity of firing the ring immediately, prompting Guilty Spark's protest that activating Halo now would destroy both the Ark and the installation, and Johnson's subsequent reply of "Deal with it" as he prepared to activate the ring. Unwilling to let "his" ring be destroyed again, Spark went rampant, attacking Johnson, SPARTAN-117, and the Arbiter. However, with the help of mortally-wounded Johnson and his laser, SPARTAN-117 managed to destroy Guilty Spark and start the firing sequence for the new Halo. Just after Johnson's final remarks to SPARTAN-117, he died, and they escaped the control room by taking Johnson's Warthog to the Forward Unto Dawn. The unstable state of the ring as it fired, the Slipspace portal collapsed as the Dawn entered it and while the forward half with the Arbiter made it to Earth, the rear half fell out of slipspace with Cortana and SPARTAN-117.

Battles
Human-Covenant War
 * Battle of Sigma Octanus IV
 * Battle of Reach
 * Battle of Installation 04
 * Raid on the Truth and Reconciliation
 * Battle of the Silent Cartographer
 * Massacre at Eridanus Secundus
 * Operation: FIRST STRIKE
 * First Battle of Earth
 * First Battle of Mombasa
 * Battle of the Gas Mine
 * Battle of Installation 05
 * Second Battle of Earth
 * Battle of Havana
 * Battle of Cleveland
 * Battle of Pawas
 * Battle of the Crow's Nest
 * Battle of Tsavo Highway
 * Battle of Voi
 * Second Battle of Mombasa
 * Battle of Onyx
 * Battle of Mare Erythraeum
 * Battle of Installation 00

The Great Schism
 * First Battle of High Charity

Quarantine of the Flood
 * Quarantine of Installation 05
 * Battle of the Quarantine Zone
 * Second Battle of High Charity

Deaths
Human
 * Governor Jacob Jiles
 * General Kits
 * Vice Admiral Danforth Whitcomb
 * Colonel Herzog
 * Captain Jacob Keyes
 * Lieutenant Commander Kurt Ambrose
 * Lieutenant Commander Miranda Keyes
 * Major Antonio Silva
 * First Lieutenant Jake Chapman
 * First Lieutenant Melissa McKay
 * Second Lieutenant Dalu
 * Second Lieutenant McCasky
 * Second Lieutenant Oros
 * Master Chief Petty Officer John-117 (Presumed dead by Fleet Admiral Hood and Arbiter Thel 'Vadam)
 * Sergeant Major Avery J. Johnson
 * First Sergeant Tink Carter
 * Master Sergeant Lister
 * Gunnery Sergeant Waller
 * Staff Sergeant Marvin Mobuto

Sangheili
 * Imperial Admiral Xytan 'Jar Wattinree (Presumed dead by the NOVA activation near Joyous Exultation)
 * Fleet Master Voro Nar 'Mantakree
 * Heretic Commander Sesa 'Refumee

San 'Shyuum
 * High Prophet of Regret
 * High Prophet of Mercy

Jiralhanae
 * Chieftain Tartarus

Forerunner
 * 343 Guilty Spark
 * 2401 Penitent Tangent (Presumed destroyed)

Flood
 * Gravemind

Trivia

 * The number 2552 is an obvious reference to the number 7|seven. $$2+5=7$$, and $$\frac{2+5+5+2=14}{2}=7$$, as well as $$25+52=77$$ in which both digits are 7.