In summary, the conversation discusses how to solve a geometric coincidence problem in MCNP, where shapes need to intersect and be defined in a specific way. The conversation also addresses a specific issue with cell definitions and the use of positive and negative surfaces. The issue is eventually resolved by correcting an error in the x-axis, but there is still a problem with cell card 1. There is also mention of a discrepancy between MCNP and VisEd in terms of displaying the model.
In a cell definition a positive surface typically means above or outside. A negative surface means below or inside. If you take a look at cell 3, you have -3 4, meaning below x=4 and at the same time above x=6. The space between x=4 and 6 is "3 -4". Now have a look at cell 4 and see if you can find something similar.
However, after I corrected the error of x axis, the modeling problem still occurred in cell card 1. Why is cell card 2 and cell card 1 written in the same way? cell1 caused the problem, but cell2 did not