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Interpenetration of solids containing plane surfaces (prism with prism, pyramid with pyramid,
prism with pyramid) results in a polygonal line or polygonal lines.
The type of intersection of surfaces depends on the types of geometric forms, which can be
two- or three-dimensional.
Solids having curved surfaces results in closed curve or curves.
The type of intersection depends on the types of geometric forms and their geometric
relationship. There are several geometric relationships:
external-contact of surfaces– Common ellement is point or line surface contact if one line on
one surface intersect the one line on other surface (Fig. 7.14);

Figure 7.14

internal-contact of surfaces–Line of intersection is criss-cross closed line (Fig. 7.15);

Figure 7.15

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