Question: Equation for the area of a triangle given unknown points of verticies - what does ~ mean?

restart;
with(geometry);

triangle(ABC, [point(A, a, b), point(B, c, d), point(C, e, f)]);
AreCollinear: hint: could not determine if a*d-a*f-b*c+b*e+c*f-d*e is zero
Error, (in geometry:-triangle) not enough information: the three points might be AreCollinear

assume(a*d - a*f - b*c + b*e + c*f - d*e <> 0);

triangle(ABC, [point(A, a, b), point(B, c, d), point(C, e, f)]);
                              ABC

area(ABC);
                   

What does the ~ after the point variables supposed to mean?

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