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It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean a finite set of points and lines such that

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

  1. every pair of points determines determines a unique line
  2. every line contains at least two points
  3. there are at least two distinct lines
  4. for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (i.e. affine planes) all lines have the same number of points, and in finite elliptic geometries in which every line contains at least 3$3$ points (i.e. projective planes) all lines have the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be {1,2,3,4,5,6}$\{1,2,3,4,5,6\}$ and let the lines be the set {1,2,3}$\{1,2,3\}$, together with all of the 2$2$-element subsets except for {1,2}$\{1,2\}$, {1,3}$\{1,3\}$, {2,3}$\{2,3\}$.

It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean a finite set of points and lines such that

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (i.e. affine planes) all lines have the same number of points, and in finite elliptic geometries in which every line contains at least 3 points (i.e. projective planes) all lines have the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be {1,2,3,4,5,6} and let the lines be the set {1,2,3}, together with all of the 2-element subsets except for {1,2}, {1,3}, {2,3}.

It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean a finite set of points and lines such that

  1. every pair of points determines determines a unique line
  2. every line contains at least two points
  3. there are at least two distinct lines
  4. for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (i.e. affine planes) all lines have the same number of points, and in finite elliptic geometries in which every line contains at least $3$ points (i.e. projective planes) all lines have the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be $\{1,2,3,4,5,6\}$ and let the lines be the set $\{1,2,3\}$, together with all of the $2$-element subsets except for $\{1,2\}$, $\{1,3\}$, $\{2,3\}$.

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Louis D
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It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean a finite set of points and lines such that

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (unique parallel linesi.e. affine planes) all lines have the same number of points, and in finite elliptic geometries (no parallel lines) in which every line contains at least 3 points, every line has (i.e. projective planes) all lines have the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be {1,2,3,4,5,6} and let the lines be the set {1,2,3}, together with all of the 2-element subsets except for {1,2}, {1,3}, {2,3}.

It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (unique parallel lines) all lines have the same number of points and in finite elliptic geometries (no parallel lines) in which every line contains at least 3 points, every line has the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be {1,2,3,4,5,6} and let the lines be the set {1,2,3}, together with all of the 2-element subsets except for {1,2}, {1,3}, {2,3}.

It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean a finite set of points and lines such that

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (i.e. affine planes) all lines have the same number of points, and in finite elliptic geometries in which every line contains at least 3 points (i.e. projective planes) all lines have the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be {1,2,3,4,5,6} and let the lines be the set {1,2,3}, together with all of the 2-element subsets except for {1,2}, {1,3}, {2,3}.

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Louis D
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It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (unique parallel lines) all lines have the same number of points and in finite elliptic geometries (no parallel lines) in which every line hascontains at least three3 points, every line has the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be {1,2,3,4,5,6} and let the lines be the set {1,2,3}, together with all of the 2-element subsets except for {1,2}, {1,3}, {2,3}.

Just to clarify, by finite hyperbolic geometry I mean

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (unique parallel lines) all lines have the same number of points and in finite elliptic geometries (no parallel lines) in which every line has at least three points, every line has the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points).

It seems to me that the answer should be yes, but my naive attempts to come up with an example have failed.

Just to clarify, by finite hyperbolic geometry I mean

i) every pair of points determines determines a unique line

ii) every line contains at least two points

iii) there are at least two distinct lines

iv) for every line L and every point p not on the line, there are at least two distinct lines which are incident with p which do not intersect L

It is easy enough to show that in finite euclidean geometries (unique parallel lines) all lines have the same number of points and in finite elliptic geometries (no parallel lines) in which every line contains at least 3 points, every line has the same number of points.

It is also easy enough to come up with an example of a finite hyperbolic geometry in which not every line has the same number of points (but some lines have exactly two points). e.g. Let the points be {1,2,3,4,5,6} and let the lines be the set {1,2,3}, together with all of the 2-element subsets except for {1,2}, {1,3}, {2,3}.

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Louis D
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