_Step
#0: The starting Sphere -- green on the outside, red on the inside.
_Step
#1: push the South Pole through the North Pole
_Step
#2: Pinch the red South Pole bulge to push its front to the back, and vice
versa.
_Step
#3: Continue the process of bulging out to the front and back, now seen
from below.
_Step
#4": Start to twist the figure-8 shaped "inner tube" at the bottom.
_Step
#5: Continue that twisting motion through about 270 degrees until the red
ear drums start to face upwards.
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#6: We are at the half-way point; this is the famous Morin surface !
_Step
#7: Push the red tube crossing the top downwards to get to the equivalent
twisted state of Step #5.
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#8: The twist of the red "inner tube" is being reduced.
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_Step
#9: The un-twisting motion has been completed; result from above and below.
_Step
#10: The front and back bulges are being retracted, to make a simple green
hump at the top.
_Step
#11: Almost done, we just need to retract the green bulge down to the South
Pole.
_Step
#12: The sphere has been turned inside out.
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A first, not all-too-successful attempt at building a physical model of
Step #3.
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A more robust model with thicker struts of Step #3 in the sequence.
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A model of Step #2 in the build phase.
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A successful model of the half-way point (Morin surface) in a different,
fully gridded style.
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And a cut-away model of the same step to show what happens inside the lobes.