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BP820 Shape can be combined with a copy of itself to form a convex shape vs. not so.
(edit; present; nest [left/right]; search; history)
CROSSREFS

For the generalization of this property, see BP991.



Adjacent-numbered pages:
BP815 BP816 BP817 BP818 BP819  *  BP821 BP822 BP823 BP824 BP825

KEYWORD

nice, precise, allsorted

CONCEPT tiling (info | search)

WORLD

fill_shape [smaller | same | bigger]
zoom in left

AUTHOR

Isaac Hathaway

BP850 Shape can be maneuvered around the corner vs. not so.
(edit; present; nest [left/right]; search; history)
REFERENCE

https://en.wikipedia.org/wiki/Moving_sofa_problem

CROSSREFS

Adjacent-numbered pages:
BP845 BP846 BP847 BP848 BP849  *  BP851 BP852 BP853 BP854 BP855

KEYWORD

nice, precise, physics, creativeexamples, proofsrequired, left-narrow, right-narrow, dithering

CONCEPT rotation_required (info | search),
imagined_motion (info | search),
physically_fitting (info | search)

AUTHOR

Leo Crabbe

BP856 Compound shape would hit the dot if rotated vs. not so.
(edit; present; nest [left/right]; search; history)
CROSSREFS

Adjacent-numbered pages:
BP851 BP852 BP853 BP854 BP855  *  BP857 BP858 BP859 BP860 BP861

KEYWORD

nice, precise, allsorted, left-narrow, preciseworld

CONCEPT imagined_motion (info | search),
collision (info | search)

AUTHOR

Leo Crabbe

BP860 Finitely many copies of the shape can be arranged such that they are locked together vs. not so.
(edit; present; nest [left/right]; search; history)
CROSSREFS

This is a generalisation of BP861.

Adjacent-numbered pages:
BP855 BP856 BP857 BP858 BP859  *  BP861 BP862 BP863 BP864 BP865

KEYWORD

hard, nice, stub, precise, stretch, unstable, hardsort, challenge, creativeexamples, perfect, pixelperfect

CONCEPT tiling (info | search)

WORLD

fill_shape [smaller | same | bigger]

AUTHOR

Leo Crabbe

BP861 Shape can be combined with a copy of itself such that they are locked together vs. not so.
(edit; present; nest [left/right]; search; history)
CROSSREFS

See BP860 for the more general version of this solution.

Adjacent-numbered pages:
BP856 BP857 BP858 BP859 BP860  *  BP862 BP863 BP864 BP865 BP866

KEYWORD

nice, precise, unstable, perfect, pixelperfect

CONCEPT tiling (info | search)

WORLD

fill_shape [smaller | same | bigger]

AUTHOR

Leo Crabbe

BP863 Two shapes can tessellate the plane together vs. not so.
(edit; present; nest [left/right]; search; history)
CROSSREFS

Adjacent-numbered pages:
BP858 BP859 BP860 BP861 BP862  *  BP864 BP865 BP866 BP867 BP868

KEYWORD

nice, precise, allsorted, math, hardsort, creativeexamples, unorderedpair

CONCEPT infinite_plane (info | search),
tessellation (info | search),
tiling (info | search)

WORLD

2_shapes [smaller | same | bigger]

AUTHOR

Leo Crabbe

BP891 Dots can be connected to create one triangle within another vs. not so.
(edit; present; nest [left/right]; search; history)
COMMENTS

Or equivalently, "3 dots within boundary of convex hull vs. not so". - Leo Crabbe, Aug 01 2020

CROSSREFS

Adjacent-numbered pages:
BP886 BP887 BP888 BP889 BP890  *  BP892 BP893 BP894 BP895 BP896

KEYWORD

nice, precise, allsorted, preciseworld

CONCEPT convex_hull (info | search),
triangle (info | search)

WORLD

6_dots [smaller | same | bigger]

AUTHOR

Cameron Fetter

BP892 Black shapes can be arranged such that they fit inside rectangular outline vs. not so.
?
(edit; present; nest [left/right]; search; history)
COMMENTS

There is a slight ambiguity here regarding whether a shape could be placed within another shape's hole. This is a question of how one perceives the Problem: are we sliding shapes around on a table in 2D or are we allowed to 'lift' them in 3D space?

CROSSREFS

Adjacent-numbered pages:
BP887 BP888 BP889 BP890 BP891  *  BP893 BP894 BP895 BP896 BP897

KEYWORD

nice, precise, perfect, pixelperfect, help

CONCEPT rotation_required (info | search),
physically_fitting (info | search)

AUTHOR

Leo Crabbe

BP897 Wide angles connected to narrow angles vs. not so.
(edit; present; nest [left/right]; search; history)
COMMENTS

Another solution is that right examples can be folded down flat onto one isosceles triangle while left examples cannot.

All examples in this Problem feature four isosceles triangles connected by corners and/or edges.

CROSSREFS

This was conceived as a false solution for BP898.

Adjacent-numbered pages:
BP892 BP893 BP894 BP895 BP896  *  BP898 BP899 BP900 BP901 BP902

KEYWORD

precise, allsorted, notso, traditional, preciseworld

CONCEPT triangle (info | search)

WORLD

[smaller | same | bigger]

AUTHOR

Molly C Klenzak, Aaron David Fairbanks

BP898 Can fold into tetragonal disphenoid ("isosceles tetrahedron") vs. cannot.
(edit; present; nest [left/right]; search; history)
COMMENTS

Which two sides are the long sides and which side is the short side, or equivalently which angles are the wider angles and which angle is the narrower angle, is the only relevant information to consider for each triangle. Triangles are all assumed isosceles and congruent to one another.


All examples in this Problem feature four of these triangles connected by corners and/or edges.

CROSSREFS

BP897 was conceived as a false solution for this.

Adjacent-numbered pages:
BP893 BP894 BP895 BP896 BP897  *  BP899 BP900 BP901 BP902 BP903

KEYWORD

hard, precise, allsorted, notso, math, preciseworld

CONCEPT triangle (info | search)

WORLD

[smaller | same | bigger]

AUTHOR

Molly C Klenzak

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