The task for ingenuity

Good day!

When I was studying to be an engineer, my lecturer of plotting painted on a board such characters here:





and promised to put Ladder someone who will build a third projection.

Well, people razoshёlsya: someone said it was a void in the cube, what it reasonably argued that in this case the edge of the hollow recesses would be indicated by dotted lines. Someone said that the outer wire cube, but in this case always have an engineer to how these figures are attached to each other. In general, both the wrong answer. On two projections - solid, monolithic body.

Please for those who guessed the answer does not lay out at once, it is obvious to let people think.

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