There is no boundary.
boundary is missing.
There are not always boundaries.
The presence of a boundary in the direction of one axis does not imply that it is bounded in the direction of another axis.
In the chronological process of A, B, C, D, the part of B and C is a phase called X. I circled only B and C in red as shown on the left
But this figure implicitly assumes that "E and F are not X".
Is that assumption correct?
https://gyazo.com/7b64d59f692e215bcceed1c39de422fe
A clear boundary in the time axis direction does not necessarily mean that there is also a clear boundary in the spatial axis direction.
The bias of easy drawing
Organizational Boundaries 　 campfire (usually large, and for gathering and singing, etc.)
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