Pith. sign in

Paper Citation Record · LEDGER

Injectivity and the Law of Demand

As of 23 August 2026, this Paper Citation Record lists 37 of 37 outbound references and 0 inbound Pith citation observations for arXiv:1908.05714.

A citation records a reference. It does not transfer a finding from one paper to another.

pith.paper-citation-record.v1
1908.05714 v1

Coverage vector

measured 37 of 37 reference resolution

Typed states for the displayed outbound observations.

Source: paper_references, paper_reference_links, observed 2026-08-14T13:15:20.021647Z

measured 37 of 37 standing notices

One-hop event checks from named stored sources.

Source: scholarly_work_events, retraction_status_cache, observed 2026-08-22T06:32:14.747728+00:00

measured 0 of 0 inbound itemization

Pith citing papers itemized under the disclosed page cap.

Source: paper_references, paper_reference_links

measured 0 of 1 external citation measurements

A source-named dated measurement, never combined with another source.

Source: cited_works

Reference resolution

37 of 37 outbound references displayed

  • verified exact0
  • verified fuzzy36
  • unresolved1
  • parse uncertain0
  • malformed identifier0
  • metadata mismatch0

External citation measurements

No source-named external measurement is stored.

Outbound references

Observation 9303e9b0-5a0a-429d-bdad-a1a2e86287e5 · outbound

This paper cites Nonparametric counterfactual predictions in neoclassical models of international trade.

Injectivity and the Law of Demand Nonparametric counterfactual predictions in neoclassical models of international trade

Reference 1

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.584682Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.844100Z digest=sha256:f7e211b9acad357004bc7f42948a177da30a568f373549641dd4f24b8097021a

Observation 3584afe8-cd3f-470b-ab27-d6fb03052494 · outbound

This paper cites Demand analysis using strategic reports: An application to a school choice mechanism.

Injectivity and the Law of Demand Demand analysis using strategic reports: An application to a school choice mechanism

Reference 2

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.565328Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.849309Z digest=sha256:51605125802bc5088825167fac4e85071d517de286960f9befbfad523ab9b06a

Observation 4d13a284-d1b1-4d0c-85c6-0002b95453cc · outbound

This paper cites Simple estimators for invertible index models.

Injectivity and the Law of Demand Simple estimators for invertible index models

Reference 3

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.547610Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.854671Z digest=sha256:6ec55f59ffddccc7fe005cd1b0887474698d42da8a937f9060c8fb837c885bcd

Observation bed1b6bb-f210-45ed-8106-781d55494025 · outbound

This paper cites Identification with additively separable heterogeneity.

Injectivity and the Law of Demand Identification with additively separable heterogeneity

Reference 4

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.528331Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.859434Z digest=sha256:c62e54e478fea11bbcd06c83d54099ba996d342cbe3f284f87cc979e1c9dc970

Observation f54fec28-61e2-4535-bd5e-68b8a881ccb8 · outbound

This paper cites On the stability of the competitive equilibrium, i.

Injectivity and the Law of Demand On the stability of the competitive equilibrium, i

Reference 5

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.511950Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.864438Z digest=sha256:52b93bfef0670e67806935119123e01cba6a093bbae25b3d2aeb889ff0cd81f8

Observation 5961986b-ee19-4961-87e2-38a5e2b5ec43 · outbound

This paper cites Some remarks on the equilibria of economic systems.

Injectivity and the Law of Demand Some remarks on the equilibria of economic systems

Reference 6

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.497816Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.870394Z digest=sha256:ef0f53202b43a17df4a2d566b9218ea953ffdaf0689357a9093af02b8118d6ae

Observation c03d62dd-0be0-4973-87fa-01e895cfaa07 · outbound

This paper cites Walrasian equilibrium in large, quasilinear markets.

Injectivity and the Law of Demand Walrasian equilibrium in large, quasilinear markets

Reference 7

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.485668Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.875751Z digest=sha256:ae4b1ab1a27041bfbf6a485d92bafa77194fadc4209811bb17596fee501d7f83

Observation 67577442-8dc1-4aa5-88b2-5358af57d137 · outbound

This paper cites Heterogeneity and the non-parametric analysis of consumer choice: conditions for invertibility.

Injectivity and the Law of Demand Heterogeneity and the non-parametric analysis of consumer choice: conditions for invertibility

Reference 8

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.472063Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.880147Z digest=sha256:59f664352d5732482e86bde6d576243572e49fdf627a5b36d19980a053f42d5e

Observation 408597f5-a2d7-49c2-b821-b27aebbff2c3 · outbound

This paper cites Automobile prices in market equilibrium.

Injectivity and the Law of Demand Automobile prices in market equilibrium

Reference 9

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.456166Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.884555Z digest=sha256:9d3d5d5e73c555bd27e4b497c8c3cb111f50376c95391f5e8187a12edac8430f

Observation 5624a661-c1d5-47be-bba7-9a88494f4196 · outbound

This paper cites Connected substitutes and invertibility of demand.

Injectivity and the Law of Demand Connected substitutes and invertibility of demand

Reference 10

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.442954Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.888882Z digest=sha256:0357ee39b188e613e8cfe988507ff3f170d1cbccdf4443edd8d2abdbd7fb60b2

Observation 2f104880-71a6-4a7f-8a16-0e26ba1242d4 · outbound

This paper cites Estimating discrete-choice models of product differentiation.

Injectivity and the Law of Demand Estimating discrete-choice models of product differentiation

Reference 11

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.426675Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.893716Z digest=sha256:34bcc00225c0a9c22e52b83db748a48774372c31ebed3e6731a6009a9357d0e6

Observation b6ea2830-ee44-4b97-b350-ddde2d878a0d · outbound

This paper cites Nonparametric identification of multinomial choice demand models with heterogeneous consumers.

Injectivity and the Law of Demand Nonparametric identification of multinomial choice demand models with heterogeneous consumers

Reference 12

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.406368Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.898953Z digest=sha256:26c443db89fd768fb565e2577308ad4a54b0ead356115083a10388db8b80bbfc

Observation 84d9319b-88ed-48d1-9747-8cde78332388 · outbound

This paper cites Identification in differentiated products markets using market level data.

Injectivity and the Law of Demand Identification in differentiated products markets using market level data

Reference 13

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.391421Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.903817Z digest=sha256:945336804306fc4c9a589f778b73e0970e6cdfc224b7b13e65590986e47c1bd7

Observation 354e5cfc-64ff-4d6d-a035-3bf33d7fa393 · outbound

This paper cites Identification of nonparametric simultaneous equations models with a residual index structure.

Injectivity and the Law of Demand Identification of nonparametric simultaneous equations models with a residual index structure

Reference 14

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.377292Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.911104Z digest=sha256:f7bfe6997953d764f463c6e72a3838da32b21fe6ace6b1bf8fc91c6f94674660

Observation 09857adc-f40f-44d4-8994-f21b5e50d1f3 · outbound

This paper cites Individual counterfactuals with multidimensional unobserved heterogeneity.

Injectivity and the Law of Demand Individual counterfactuals with multidimensional unobserved heterogeneity

Reference 15

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.364107Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.918627Z digest=sha256:d30efdda7001b1f0490a17fc78865cefcbf2466d9022da6ddf4ede9a103f0acc

Observation 8e6a4747-d654-4519-9df9-313aff0396bb · outbound

This paper cites Yogurts choose consumers? identification of random utility models via two-sided matching.

Injectivity and the Law of Demand Yogurts choose consumers? identification of random utility models via two-sided matching

Reference 16

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.351702Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.925450Z digest=sha256:21057b4815a76221a2d731088c70ba3ea5ea5dc75674611bed350ad6770ceea5

Observation fad25524-baec-4e18-a68d-3a282c6f1624 · outbound

This paper cites The nonparametric approach to applied welfare analysis.

Injectivity and the Law of Demand The nonparametric approach to applied welfare analysis

Reference 17

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.338671Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.931823Z digest=sha256:bbdca18f904cfdd28dece5fd803e79da354f09e004f012799987d43939fbf642

Observation 994f7d13-5c93-4021-a21d-6edc79e03e86 · outbound

This paper cites Estimation of nonparametric functions in simultaneous equations models, with an application to consumer demand.

Injectivity and the Law of Demand Estimation of nonparametric functions in simultaneous equations models, with an application to consumer demand

Reference 18

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.324608Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.937295Z digest=sha256:803ba3ae2d926f05267148b8ad0c008049222c40105a1d3e2d1d458e1172c9f4

Observation 4269fbbc-88cf-4655-a1d5-b9aebd73cab0 · outbound

This paper cites Generalized instrumental variable models.

Injectivity and the Law of Demand Generalized instrumental variable models

Reference 19

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.311350Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.944451Z digest=sha256:97e1fa68743346f40886035952c00d01f893869694a89c7132353ac96d64fb69

Observation 30bb2194-74f1-4d0d-9758-a83b3effa059 · outbound

This paper cites On the nonparametric identification of multiple choice models.

Injectivity and the Law of Demand On the nonparametric identification of multiple choice models

Reference 20

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.299129Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.948878Z digest=sha256:903e7d48ff7fdf930c40dd8d03a3f49a81ecfdb5848b8f8cf31cdfd9c4c09305

Observation 3fbdc02e-1fba-44ff-95d4-695cb49e375b · outbound

This paper cites Demand models for differentiated products with complementarity and substitutability.

Injectivity and the Law of Demand Demand models for differentiated products with complementarity and substitutability

Reference 21

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.285444Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.954236Z digest=sha256:6a96c7e4a87032c1e3986e01e7f00fd46c54eebc823bd4f72dc9711e9c667ec3

Observation 0531c8b5-ec84-4dc6-ba07-80251bdd3cc6 · outbound

This paper cites Unobserved heterogeneity in matching games.

Injectivity and the Law of Demand Unobserved heterogeneity in matching games

Reference 22

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.270250Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.960062Z digest=sha256:638200797fefe45cae192845efb54c6f1881d96e426e2d308bfaccd4565eb6f2

Observation 4c76e551-9bfb-448e-9b77-cfe83a7d58d9 · outbound

This paper cites The jacobian matrix and global univalence of mappings.

Injectivity and the Law of Demand The jacobian matrix and global univalence of mappings

Reference 23

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.255727Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.964369Z digest=sha256:837bf7ce2b2c992815ff1b04d8280bc628e672ab37c94a29eea47df5d9098fd8

Observation 3659b181-a94c-4ade-b21d-6df0a16ab610 · outbound

This paper cites Valuing new goods in a model with complementarity: Online newspapers.

Injectivity and the Law of Demand Valuing new goods in a model with complementarity: Online newspapers

Reference 24

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.240795Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.968237Z digest=sha256:dc8036f2bb0ba47f37e0be40d258eb7c1934db60ca52762549a0cf97417bf83b

Observation fef1eea3-6c2f-4f14-9598-9c98ac73b55d · outbound

This paper cites law of demand.

Injectivity and the Law of Demand law of demand

Reference 25

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.227221Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.972939Z digest=sha256:6cc9625f68806f9c3481f168874450d2092568501917ce5bd1e4dedc3fb7fe0a

Observation 2c459a91-e3c2-4f38-aea7-d2c4ea45a529 · outbound

This paper cites On convexity of preimages of monotone operators.

Injectivity and the Law of Demand On convexity of preimages of monotone operators

Reference 26

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.213095Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.977230Z digest=sha256:44aee57c8a9e589cc64742b34a259377b717e5be0654fdc454992430a60034e9

Observation 270d81f9-6106-4624-b950-3fb97ed392d8 · outbound

This paper cites On injectivity of a class of monotone operators with some univalency consequences.

Injectivity and the Law of Demand On injectivity of a class of monotone operators with some univalency consequences

Reference 27

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.196840Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.981052Z digest=sha256:b2feb5d3073ebf3e0becd3806f6d4593b2d9c5f3192f030d1427a17373e8ecbd

Observation a1b28777-635e-48e9-be12-44eb89526090 · outbound

This paper cites On the uniqueness of equilibrium once again.

Injectivity and the Law of Demand On the uniqueness of equilibrium once again

Reference 28

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.183364Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.984356Z digest=sha256:c6459cc2c5949402e13648fb7a613c42a51e0ed87d90fb7bbdb7002b7d7b95e2

Observation 180bcbdc-a923-4f07-9631-a7f754d21c8e · outbound

This paper cites Identification in nonparametric simultaneous equations models.

Injectivity and the Law of Demand Identification in nonparametric simultaneous equations models

Reference 29

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.169192Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.988191Z digest=sha256:273b09732c076ee4eef3ee26ad53b327e43380ec667920dd694cd3a62b0fec85

Observation a0cef305-c545-485f-a0bf-b94023f5539b · outbound

This paper cites Estimation of nonparametric models with simultaneity.

Injectivity and the Law of Demand Estimation of nonparametric models with simultaneity

Reference 30

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.155548Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.992044Z digest=sha256:4d05163501567d384b014bef32b111ab47d47e3f8b6c636f745be14574dd85b8

Observation cb58ded1-678e-4883-9211-511d6cee75d3 · outbound

This paper cites Econometric models of probabilistic choice.

Injectivity and the Law of Demand Econometric models of probabilistic choice

Reference 31

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.141051Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.995842Z digest=sha256:bca7dd9fdd1c5cc68102e2c11b3727c17f28e240f22f64a5ca51f285f78f7461

Observation 555836c8-59b7-458c-83a2-d019dea9bae1 · outbound

This paper cites On p-and s-functions and related classes of n-dimensional nonlinear mappings.

Injectivity and the Law of Demand On p-and s-functions and related classes of n-dimensional nonlinear mappings

Reference 32

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.127001Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:19.999890Z digest=sha256:7e289f9b3aa115cbbda4b172b06271539400c6218091460432618f501d300eab

Observation 0a1ee4b5-687f-4643-b009-b1fe87284c5a · outbound

This paper cites On the surjectivity of the mapping between utilities and choice probabilities.

Injectivity and the Law of Demand On the surjectivity of the mapping between utilities and choice probabilities

Reference 33

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.111346Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:20.004018Z digest=sha256:db9cc1e95c92ba3086f23c875abde8324115ac2a274a289a6c4b21b5699d3326

Observation bbf8f965-be54-4d26-91df-06aa9dee80b5 · outbound

This paper cites On global univalence theorems, volume 977 of Lecture Notes in Mathematics.

Injectivity and the Law of Demand On global univalence theorems, volume 977 of Lecture Notes in Mathematics

Reference 34

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.098308Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:20.007758Z digest=sha256:d5ca8ed34812ffdd440ae5fb733b9213345ee8bcc4b06293fc37f2e252796190

Observation f4225870-8782-4d09-8b99-61e0fb895f4c · outbound

This paper cites Convex Analysis.

Injectivity and the Law of Demand Convex Analysis

Reference 35

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.084852Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:20.012176Z digest=sha256:1804a1daab02a4d421603987a8939c100dbe7f5886c6118128f87578d96113cf

Observation 4f906b31-28e2-4421-9a75-c766abf094ef · outbound

This paper cites Variational analysis, volume 317.

Injectivity and the Law of Demand Variational analysis, volume 317

Reference 36

Resolution
unresolved
no resolver link, observed 2026-08-14T13:15:20.016039Z

Source-reported events for the cited work

Unavailable: canonical work link unavailable.

source=arxiv_source observed=2026-08-14T13:15:20.016039Z digest=sha256:d7c51481b75825cab3ac00a06191c9130c7e6695a386ed6640e456a84a8b23b6

Observation fdb053bb-531f-4343-bd53-98751525760a · outbound

This paper cites Estimating semi-parametric panel multinomial choice models using cyclic monotonicity.

Injectivity and the Law of Demand Estimating semi-parametric panel multinomial choice models using cyclic monotonicity

Reference 37

Resolution
verified fuzzy
raw_fallback, observed 2026-08-14T13:15:20.062161Z

Source-reported events for the cited work

No event found in the named queried sources as of 2026-08-22T06:32:14.747728+00:00.

source=arxiv_source observed=2026-08-14T13:15:20.021647Z digest=sha256:620d65ff0f2752ca62ae7d91708e069b2d2cf7213359e39ced6aa126498426dd

Pith citing papers

No inbound Pith citation observations are available.