Typed states for the displayed outbound observations.
Source: paper_references, paper_reference_links, observed 2026-08-07T15:39:45.266943Z
Paper Citation Record · LEDGER
As of 8 August 2026, this Paper Citation Record lists 88 of 88 outbound references and 0 inbound Pith citation observations for arXiv:2505.14519.
A citation records a reference. It does not transfer a finding from one paper to another.
Typed states for the displayed outbound observations.
Source: paper_references, paper_reference_links, observed 2026-08-07T15:39:45.266943Z
One-hop event checks from named stored sources.
Source: scholarly_work_events, retraction_status_cache, observed 2026-08-08T06:32:00.761636+00:00
Pith citing papers itemized under the disclosed page cap.
Source: paper_references, paper_reference_links
A source-named dated measurement, never combined with another source.
Source: cited_works
88 of 88 outbound references displayed
External citation measurements
No source-named external measurement is stored.
Observation 39039ba6-6e94-439c-ada2-eaba6ceaf951 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 1
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 19d297a3-da11-40d2-9a56-2bd913710ec2 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 2
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 66523f18-d05a-4f8c-9742-9f346f7cbff1 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 3
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation c8da54eb-4324-4d23-9007-bf49deb6375a · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 4
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation b4c702d8-ca2d-4988-a971-e3d9452e56cf · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 5
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation ce2ee54b-4d66-420d-ba9a-c8711178f855 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 6
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 7235a885-509d-410c-8dad-bbb395a00bc9 · outbound
Distributed quantum computing with black-box subroutines Wang, Universal quantum computing models: a perspective of resource theory, Acta Phys
Reference 7
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation daafee35-6de7-4ffb-9370-ab49df37a1d4 · outbound
Distributed quantum computing with black-box subroutines Caleffi, M
Reference 8
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 9997f9f4-c55c-4372-90fe-c6d484deda29 · outbound
Distributed quantum computing with black-box subroutines Barral, F
Reference 9
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation f6883e73-d84b-448b-acee-831dda193c94 · outbound
Distributed quantum computing with black-box subroutines Broadbent, J
Reference 10
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 080e112c-cb1a-4ba1-8684-c332fc4d5f66 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 11
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation f993c5e4-4f06-4c95-8d8b-68dc34776b15 · outbound
Distributed quantum computing with black-box subroutines Wang, Choi states, symmetry-based quantum gate teleportation, and stored-program quantum computing, Phys
Reference 12
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation fd602921-e2dc-4b64-b64c-b020638daa89 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 13
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation cd433616-d0fc-44ea-8ade-87fc36ea89c0 · outbound
Distributed quantum computing with black-box subroutines Wang, A family of quantum von Neumann archi- tecture, Chin
Reference 14
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 73d6930d-93ba-4102-99e0-65bc4dd8efab · outbound
Distributed quantum computing with black-box subroutines Avron, O
Reference 15
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation d08b0de2-0e09-4e4c-b764-ba36bd1ed70d · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 16
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation ab45e293-fba0-4efa-988c-d9a51b405a1f · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 17
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation ec8d643d-d386-42d5-abe4-76d532aa6dfd · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 18
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 1ee507ee-7d2b-4c15-a125-c39abdefe202 · outbound
Distributed quantum computing with black-box subroutines Hwang, H.-T
Reference 19
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 5f7df599-f583-4670-8c6f-93b49c341054 · outbound
Distributed quantum computing with black-box subroutines Piveteau, D
Reference 20
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation b2a5f5d4-454a-4828-8410-589a87366e01 · outbound
Distributed quantum computing with black-box subroutines Ufrecht, M
Reference 21
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation ce31b92b-5b79-4d72-8fa7-2457b63c58c2 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 22
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation f5525d79-7a27-42b8-b3bd-4260b4b2feee · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 23
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 81f3bc12-87c2-4bb6-b04f-3abcf919de00 · outbound
Distributed quantum computing with black-box subroutines Almanakly, B
Reference 24
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation be2dd408-ee4d-467b-a01a-2575086bb333 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 25
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation a6fbd327-e8e0-4156-bd3e-cad896b5d314 · outbound
Distributed quantum computing with black-box subroutines Andres-Martinez, T
Reference 26
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 3e146dc9-3fce-4f65-bced-721603902ddf · outbound
Distributed quantum computing with black-box subroutines Luo, Y.-Z
Reference 27
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation ef151516-7c94-4f3d-9914-6cc3e3f7d762 · outbound
Distributed quantum computing with black-box subroutines Hayashi, Quantum Information Theory: Mathemati- cal Foundation, 2nd edition, Springer, 2017
Reference 28
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 67ff595c-7110-44c8-a811-773b8305314c · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 29
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation b9995fde-f2f2-4705-bcbf-934073a80687 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 30
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation c1c7cd11-9e03-430c-bffd-31e9b2e6e4fb · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 31
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 9bbf1e4d-896d-4862-9e5a-6765e2810644 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 32
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 12af3004-a9cd-48ae-b90f-094b61dc4c78 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 33
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation f8ad2a02-634e-467d-9097-a0e0009a5dea · outbound
Distributed quantum computing with black-box subroutines Dieks, Communication by EPR devices, Phys
Reference 34
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 7cbd16c9-ad3f-4906-862e-2c760b8d39ba · outbound
Distributed quantum computing with black-box subroutines Mayers, Unconditionally secure quantum bit commit- ment is impossible, Phys
Reference 35
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 22623630-c9b9-49cc-aef9-de2c1aa4463f · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 36
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 1c351676-b376-4466-be50-3c00e1bf1dfe · outbound
Distributed quantum computing with black-box subroutines Araujo, A
Reference 37
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 21760a06-dc9c-4d1e-8e38-d56f83b1eae7 · outbound
Distributed quantum computing with black-box subroutines Oszmaniec, A
Reference 38
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation a343a701-cd91-43f9-a3ee-638421e72ba3 · outbound
Distributed quantum computing with black-box subroutines Thompson, K
Reference 39
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 911004e0-0532-42c5-a293-6080477a17e1 · outbound
Distributed quantum computing with black-box subroutines Wehner, C
Reference 40
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation eef99092-356d-4724-97d7-dda9c2cc0b2f · outbound
Distributed quantum computing with black-box subroutines Wang, A prototype of quantum von Neumann ar- chitecture, Commun
Reference 41
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation e55e3ed2-62ac-4d85-a45c-5424ee8fe5b3 · outbound
Distributed quantum computing with black-box subroutines Chiribella, G
Reference 42
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation da2d5238-1374-4ae4-8045-ff96877f95ff · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 43
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation a69f5e8b-4d80-4497-9de9-81238df93454 · outbound
Distributed quantum computing with black-box subroutines Kraus, States, Effects, and Operations: Fundamental Notions of Quantum Theory, Vol
Reference 44
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 1d2cdd80-428a-4376-8881-4fc626e20d55 · outbound
Distributed quantum computing with black-box subroutines Choi, Completely positive linear maps on complex matrices, Linear Algebra Appl
Reference 45
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 94e7c605-f08d-4cc4-b248-7a08fed30b5a · outbound
Distributed quantum computing with black-box subroutines Jamio lkowski, Linear transformations which preserve trace and positive semidefiniteness of operators, Rep
Reference 46
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 9953b92e-4ee2-476c-9efc-c3bee4af5681 · outbound
Distributed quantum computing with black-box subroutines Wang, Weak, strong, and uniform quantum simu- lations, Phys
Reference 47
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 8ed9fd80-2091-4860-91a0-c37b6cd07b67 · outbound
Distributed quantum computing with black-box subroutines Yoshida, A
Reference 48
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 87094b0e-386b-4056-bb71-451ab97e10af · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 49
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 41986123-bd6e-424b-be6b-1ec7a6ecaf44 · outbound
Distributed quantum computing with black-box subroutines Aharonov, A simple proof that toffoli and hadamard are quantum universal, arXiv preprint arXiv:0301040 (2003)
Reference 50
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 065f5ec3-ea8a-4e25-8191-7af13bb41421 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 51
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 18654141-1442-4699-be71-0b72cc489d8a · outbound
Distributed quantum computing with black-box subroutines Gottesman, I
Reference 52
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 0e7ffc02-2da7-4711-894f-492a5c01ab5a · outbound
Distributed quantum computing with black-box subroutines Bravyi, A
Reference 53
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation b8e0c572-5318-45f5-b16b-cda2a003a0e1 · outbound
Distributed quantum computing with black-box subroutines Knill, R
Reference 54
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 4ef08795-b8ac-450d-8183-93ba3316b6d2 · outbound
Distributed quantum computing with black-box subroutines Kitaev, A
Reference 55
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation a9c254ba-6005-4a58-a0c6-f0e235aadd56 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 56
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 14797ce0-2e99-4ea0-9e79-af585c8015c7 · outbound
Distributed quantum computing with black-box subroutines Buhrman, R
Reference 57
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 1b159735-897b-4623-9f78-5cf7e3218d03 · outbound
Distributed quantum computing with black-box subroutines Brassard, P
Reference 58
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 116867ee-ac3c-4132-a8c0-ec5ccb914688 · outbound
Distributed quantum computing with black-box subroutines Gilyen, Y
Reference 59
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation c9adeca4-3f3f-4431-b9a3-77ceec78090b · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 60
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 70da5fa4-04dc-468c-9581-f084403e3d18 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 61
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 5e888fe7-bfc4-4cd8-ac75-390a4fe444fa · outbound
Distributed quantum computing with black-box subroutines Levine, A
Reference 62
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation b96980ed-0363-42c4-9699-0672b4e938e1 · outbound
Distributed quantum computing with black-box subroutines Khazali, K
Reference 63
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation e08a5c62-5df6-47c1-af87-e91d9a101939 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 64
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 5d0dcbb2-19c8-4567-bc01-bc0cba8844c8 · outbound
Distributed quantum computing with black-box subroutines Barenco, C
Reference 65
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation cb09ef18-a667-456b-b1e3-b1722fac9ef6 · outbound
Distributed quantum computing with black-box subroutines Saeedi, I
Reference 66
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation a67c9491-dad0-4d81-834c-2220d9bf4d66 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 67
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 27c51da1-e6bb-48c8-add5-7b9065b88d02 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 68
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 55cc246f-4fa1-4912-8a7c-d901749a1d29 · outbound
Distributed quantum computing with black-box subroutines The singlet-triplet and exchange-only flopping-mode spin qubits
Reference 69
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 8020e212-eac9-4094-8e45-283341f4be00 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 70
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 202b376f-5bc6-4564-b0cc-6b335be65625 · outbound
Distributed quantum computing with black-box subroutines Bluvstein, S
Reference 71
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation c701e895-1bcd-47af-a612-fc662641f801 · outbound
Distributed quantum computing with black-box subroutines Raussendorf, H
Reference 72
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation c22851ca-29ce-4a9a-8765-6ba7a30ed711 · outbound
Distributed quantum computing with black-box subroutines Knill, R
Reference 73
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation ca98b252-4791-4184-a165-76e174396f2b · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 74
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation c19510c5-9ae9-4917-80d4-c54cad136603 · outbound
Distributed quantum computing with black-box subroutines Photonic Quantum Computers
Reference 75
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation fecc8b99-76cb-4dcc-a037-d49a84bdd471 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 76
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 3986a424-bfa1-4496-a3ba-2625cc0b0669 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 77
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation 472d7d8f-4473-4aaa-8636-020b1d86b545 · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 78
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 7bf695bf-fbc5-41a4-a444-05eb3fdef4d6 · outbound
Distributed quantum computing with black-box subroutines ˙Zukowski, A
Reference 79
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 14423922-7b36-451f-92dd-709121fa895b · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 80
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation c3b15cfd-97ac-46bf-831f-766310a793f7 · outbound
Distributed quantum computing with black-box subroutines Chiribella, G
Reference 81
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 8b402c96-98d1-4fd3-8c06-ecd26c75608c · outbound
Distributed quantum computing with black-box subroutines Oblivious Quantum Computation and Delegated Multiparty Quantum Computation
Reference 82
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 2cecd921-c48d-4235-a999-3baaddbc0aae · outbound
Distributed quantum computing with black-box subroutines Morris, V
Reference 83
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 4842f4c5-f6dc-47a9-9434-1ee27cba8552 · outbound
Distributed quantum computing with black-box subroutines Cr´ epeau, D
Reference 84
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 87269fa2-babb-4305-8991-9573abb7cfde · outbound
Distributed quantum computing with black-box subroutines Sebastian, M
Reference 85
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 9c19735e-5698-447a-88b9-f5d3f32927df · outbound
Distributed quantum computing with black-box subroutines Wang, D.-S
Reference 86
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 83e86c2f-9ca6-472c-8c5b-370190fcbc5a · outbound
Distributed quantum computing with black-box subroutines Unresolved cited work
Reference 87
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
Observation 43509600-0ea4-45a6-898f-3e8fa725f837 · outbound
Distributed quantum computing with black-box subroutines Watrous, The Theory of Quantum Information, Cam- bridge University Press, 2018
Reference 88
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-08T06:32:00.761636+00:00.
No inbound Pith citation observations are available.