The verify[function_shells] function verifies the approximate equality between to function plots.

The parameters, P and Q, are assumed to be either PLOT data structures, sets or lists of CURVES data structures, or a CURVES data structure.

The verify(P, Q, function_shells) returns true for CURVES data structures P and Q if the points of each curve fall within an epsilon shell of a linear piecewise interpolation of the points of the other curve.

The points in the CURVES data structure must be in order and the x-coordinates must be monotonically increasing.

If P or Q are PLOT data structures or sets or lists of CURVES data structures, it checks that for each CURVES data structure in either P or Q, there exists a CURVES data structure in the other set which matches it.

This procedure does not compare any other features of the PLOT or CURVES data structures.